Thunder Sea

The Thunder Sea: The World Beneath The Waves

The people of the Five Nations only think of the world in terms of the things they’ve seen, the lands they can visit. Forests and farmland, valleys and hills. But there’s another world a Brelish farmer can’t even imagine, a land of wonders a league below the water’s surface, lit by bioluminescence and cold fire. This is no empty wilderness. There are civilizations in the oceans, cultures older than even those of the giants of Xen’drik. Eberron is home to ten seas, as diverse as the continents of the world above. Each of the seas is home to powerful nations, deadly creatures, and hidden secrets. This section focuses on the Thunder Sea, beginning with an overview of the region and delving into the major cultures found there.
In general, there’s little traffic between the people who dwell on land and those who live in the ocean depths. Just as a common Brelish farmer cares little about the ocean’s denizens, a typical merfolk kelp-tender knows nothing of Breland and has no interest in the surface dwellers. But anyone who sails the Thunder Sea needs to know what—and who—lies below.
The nations of the depths maintain their borders like any other nation, and someone who blunders into the Eternal Dominion without proper authorization faces sahuagin wrath. Most major port cities—including Sharn and Stormreach—host representatives of nearby aquatic nations, and envoys on the docks can help plan and authorize travel through their domains. As a result, most sailors know at least a little about the cultures of the waters they pass through, and every Lyrandar crew includes a “sea speaker” who knows Sahuagin and Aquan.

Open Waters

The Thunder Sea lies between Khorvaire, Xen’drik, and Aerenal. It takes its name from the unnatural storms that rage over some areas, never-ending tempests fueled by the elemental power of Lamannia. As dangerous as these waters are, this is a crucial crossroads for trade, and there’s a constant stream of ships flowing between Sharn, Stormreach, and Pylas Talaer. It’s here that the sahuagin first arose, the seat of their greatest civilization.
In the dawn of time, the Thunder Sea was the domain of the Lurker in Shadow. This overlord embodies the fear of the unknown, of the evil that could be lurking just beyond sight, and the fear that our friends could be secretly scheming against us. The Lurker created the aboleths, who conquered and dominated creatures of the deep—giants, dragons, and sahuagin. The struggle against the overlords played out beneath the water just as it did above. Dragons battled krakens and giants fought aboleths, while the sahuagin consumed the fallen on both sides. The wrath of the Lurker shattered the ocean floor. Dragons were impaled on spires of demonglass. But in time, the overlords were bound and the aboleths fled into the deepest abysses.
Today, the sahuagin of the Eternal Dominion are spread far and wide across the floor of the Thunder Sea. Their mightiest cities are built around—and into—massive slumbering creatures known as kar’lassa, “great dreamers.” The merfolk live in the upper waters above the sahuagin. Their permanent settlements are tied to manifest zones, and they perform rituals to contain the threat posed by these zones. The other major power in the Thunder Sea is the Valraean Protectorate, the domain of the sea elves. These elves laid claim to the waters around Aerenal, conquering the local sahuagin and other species, and bending them to their will. The Dominion sahuagin despise the Valraean elves, but thus far, the power of the Undying Court has repelled every assault.

Ports and Travel

The Thunder Sea is a critical path for trade. Any traffic with Xen’drik crosses the Thunder Sea. In addition to the ships of House Lyrandar (both elemental galleons with dragonmarked captains and mundane ships licensed by the house), the Thunder Sea sees traffic from Aerenal, Zilargo, Breland, and Riedra. The most important ports include Pylas Maradal (Valenar), Pylas Talaer (Aerenal), Sharn (Breland), Stormreach (Xen’drik), Trolanport (Zilargo), Wyvernskull (Darguun), and Zarash'ak (Shadow Marches Marches).
These major ports see both commercial, diplomatic, and military traffic. Aereni merchants carry shipments of exotic lumber, Riedran vessels are laden with crysteel and dragonshards, Lyrandar ships carry all manner of trade goods, and smugglers sneak barrels of kuryeva and tilxin blood into hidden coves. While the standard map of Khorvaire focuses on these major ports, there are also countless smaller ports and fishing villages scattered along the coastline.
The masters of the Thunder Sea—the sahuagin—don’t want dryskins blundering through their territory. Traveling directly along the coastline is reasonably safe, and local fisherfolk don’t need to negotiate with sahuagin every time they set sail; the sahuagin don’t lay claim to the waters within 6 miles of Khorvaire’s coast, and permit fishing an additional 20 miles beyond that. But crossing the Thunder Sea is an entirely different story. Setting aside the territorial claims of the sahuagin, the sea is filled with deadly hazards—endless storms, demonglass spires, and hungry monstrosities.
The Eternal Dominion has established specific routes that captains must follow, safe from hazards and monitored by the Dominion. Captains who wish to use these routes must obtain beacons of passage—common magic items that tell the sahuagin their travel is authorized, charged to last for a set time. Even with a beacon, there are places—such as Shargon’s Teeth—where a wise captain pays for the services of a sahuagin or merfolk guide.
Some brave (or foolish) souls deviate from these approved routes, whether desiring speed or avoiding the cost of local customs and the price of a beacon. The Thunder Sea is nearly the size of Khorvaire itself, and the sahuagin aren’t everywhere; however, those regions shunned by the sahuagin and merfolk are usually avoided with good reason, and smugglers may face dangerous environmental hazards or hungry monstrosities.

The Power of Lamannia

The storms of the Thunder Sea are legendary. Beyond wind and rain, tales speak of maelstroms that drag down even the largest vessels and masses of vegetation that rise from the water to entangle ships. All of these are very real threats, even more so because these dangers don’t obey simple laws of wind and water. The Thunder Sea is home to a wide range of manifest zones, but the most powerful and numerous are those tied to Lamannia. The endless fury of the First Storm lashes ships with lightning and storm winds, and great maelstroms can pull a ship down into the Endless Ocean. The vast masses of vegetation are tied to the Twilight Forest, fueling unnatural growth that can latch onto a vessel and trap it in the sargassum. Though the influence of Lamannia is most strongly felt here, it’s also possible to find an unexpected region of icebergs surrounding a manifest zone tied to Risia, boiling waters around a Fernian zone, or a region tied to Mabar where the shadows of sailors turn on the living.
As any skilled ocean navigator can tell you, manifest zones are stable, physical locations. While a manifest zone’s influence extends beyond its focal point, the worst storms of the Thunder Sea remain confined to specific areas. However, when the plane linked to a manifest zone is coterminous, its impact is dramatically enhanced, with storms extending beyond their usual radius and becoming far more powerful. This is why knowledge of the sea is vitally important for sailors; if you venture off the approved trade routes, you need to chart a course that will avoid the storms.
Lamannian manifest zones often release elementals into Eberron. An eternal storm may contain air elementals, while water elementals can be found in the region around a maelstrom. Such elementals aren’t intentionally cruel, but they’re driven to express their elemental drives—which often makes them dangerous to ships, which they perceive as alien invaders. Manifest zones can also produce dire beasts—octopi, sharks, and other creatures of remarkable size.
The merfolk of the Thunder Sea (discussed in more detail later in this section) serve as planar shepherds, tending manifest zones and helping to contain and mitigate their effects. This isn’t absolute; the merfolk can’t entirely disperse the power of the First Storm, or stop the growth of the Twilight Forest. But they seek to direct it, choosing to vent its power at times when there is minimal danger to innocents. Even when a region has especially bad storms due to a manifest zone, those storms could be far, far worse if the merfolk stopped performing their rituals or were driven away entirely.

The Teeth

Throughout the sea, vast spires of stone and coral rise up from the bottom of the ocean—in some cases, over a mile in height. Some reach the surface, while other clusters lie hundreds of feet below it. While these spires formed naturally, they’re often interspersed with a more dangerous—and unnatural—substance. Demonglass is similar to obsidian, but virtually indestructible. These demonglass spires—commonly called “needle teeth”—can pierce the hull of a swiftly moving ship despite being just a few inches in width. The spires in this region were created by the Lurker in Shadow during the First War (though it wasn’t responsible for the demonglass found elsewhere in Eberron, such as Ashtakala in the Demon Wastes).
The region known as Shargon’s Teeth— a Common adaptation of the Sahuagin name for the Devourer—lies directly between Sharn and Stormreach, and is the most infamous manifestation of these hazardous needle teeth. Stone spires and demonglass spikes of all sizes are scattered between this chain of islands. Only the most seasoned navigators can plot a course through the Teeth without the help of a sahuagin guide; as a result, the islands have long been a haven for smugglers and pirates, preying on ships that founder on the Teeth.
Throughout the Thunder Sea, needle teeth are a dangerous hazard for those who stray from the established trade routes—but they also provide an opportunity to interact with creatures of the sea. Any number of aquatic monstrosities may make a lair in the upper reaches of a spire. The sahuagin also often colonize the larger teeth, carving tunnels throughout a spire. High teeth thus serve as outposts projecting up to the upper waters where light can reach, allowing travelers to visit a sahuagin outpost without having to descend to the absolute depths.

Kar'lassa: The Great Dreamers

The greatest wonders of the Thunder Sea lie deep below the surface, all but unknown to the people of Khorvaire. The kar’lassa are enormous beasts—miles in length—half-buried and sleeping in the floor of the Thunder Sea. Not even the dragons of Argonnessen know the origin of the kar’lassa. They’ve slept since the beginning of recorded history, and are immune to all forms of divination magic. They could be creations of Khyber trapped before they could rise to the surface, or they could’ve been crafted by Eberron to guard against some future threat. Perhaps they are young progenitors, and when they finally wake, they will create new worlds.
All that’s known for certain is that the kar’lassa are massive, immortal monstrosities . . . and that each is bound to one of the planes. Each kar’lassa radiates the effects of a powerful manifest zone, extending up to 13 miles. The appearance of each kar’lassa reflects the plane they’re tied to; the kar’lassa of Shavarath is a massive draconic beast with steel scales, while the kar’lassa of Fernia is a serpent of embers, water forever boiling against its skin. But the strangest aspect of the kar’lassa is their dreams. As described in chapter 5, when mortals dream, their spirits are usually drawn into Dal Quor. However, when the kar’lassa dream, they don’t dream in Dal Quor. Instead, each kar’lassa dreams in the plane it’s tied to— and more wondrous yet, each great dreamer draws in the spirits of dreaming mortals. Any creature that dreams within 13 miles of a kar’lassa—including unwary sailors passing above, if any are bold enough to go off the approved travel routes—is pulled into the behemoth’s dream, instead of dreaming in Dal Quor. So, for example, anyone who sleeps in the Dominion city of Hal’iri dreams their dreams in Irian. While dreaming in this way, a creature is only present as a spirit, and is immune to the negative environmental effects of that plane; so a mortal dreamer isn’t hurt by the extreme heat of Fernia or the cold of Risia. Even if a dreamer dies in their dream from other causes, they just wake up. This is still dreaming; unless the dreamer is capable of lucid dreaming, they have little control of their actions and will likely only remember fragments of the experience. But if they do have tools or training that allow lucid dreaming (as with the uul’kur in chapter 7), this can be an interesting way to explore the planes.
Twelve kar’lassa have been discovered; one for each plane, aside from Dal Quor. The sahuagin of the Eternal Dominion have built their largest cities around eight of these great dreamers, though they’ve shunned the kar’lassa associated with Mabar, Xoriat, Thelanis, and Risia. The sahuagin harvest biomatter from the kar’lassa, and these substances are the fuel that drives their industry.
The kar’lassa are a source of wonder, not monsters to be fought. To all tests, they appear to be immortal, and regenerate damage quickly. Spells such as stone to flesh or disintegrate only work on a tiny sliver of the kar’lassa, and even that’s quickly restored. If one of these ancient slumbering monstrosities were to rise, it would be an almost unstoppable force of destruction, and destroy the Dominion city in the process. If one of these vast creatures emerged onto land, it could easily devastate cities without even meaning to.
Titanic, unstoppable monstrosities that could threaten entire cities? That sounds a little like the tarrasque. And indeed, a simple way to introduce the tarrasque into Eberron is to present it as a kar’lassa rising from its slumber and threatening Sharn or Stormreach; just add the effects of a manifest zone to the region around it. The tarrasque is small for a kar’lassa; most are miles long, large enough that the sahuagin build cities around them. But it’s possible a small kar’lassa might be the first to wake—can the heroes who oppose it find a way to return it to its slumber before the others wake? If a DM chooses to explore this plotline, they’ll have to decide the truth about the origins of the kar’lassa. If they’re the children of Eberron, they might not want to destroy innocent creatures; they could have an important purpose as yet unfulfilled. On the other hand, if they’re tools of the overlords or the Devourer, their rising will spell disaster.

Haunted Ruins and the Deepest Darkness

The Thunder Sea is vast and ancient. The sahuagin call their civilization the Eternal Dominion, but in truth, it’s risen and fallen multiple times. The Lurker, as well, has nearly risen several times, and aboleths have set the sea devils against one another in vicious civil wars. There are a handful of storm giants in the depths, but any nation they once possessed was destroyed long ago. Remnants of these conflicts are spread across the Thunder Sea. Explorers could find an ancient temple haunted by the ghosts of the storm giants that built it, an overgrown sahuagin fortress from a previous age of the Dominion, or the tomb of a dragon sealed tens of thousands of years ago. Most dangerous of all are the deepest abysses, strongholds of the surviving servants of the Lurker in Shadow. These cracks in the ocean floor might hold mighty artifacts forged during the Age of Demons, but they’re home to aboleths, fiends, and even more terrifying creatures.

What Roams The Sea?

When dealing with the Thunder Sea, remember that it’s just as civilized as the Five Nations. It does have wilderness regions with feral beasts roaming at will, and you might find wild plesiosaurs, a scheming sea hag, or a hungry scrag. But in the areas above and around sahuagin city-states, such beasts have been tamed or destroyed. All cultures of the Thunder Sea farm fish like the people of the land farm sheep or cattle; a pod of whales may be carefully managed and cultivated, and their farmers will be quite angry with dryskins who poach their ichthyic livestock. There are sharks—and giant sharks—in the wild waters, but in the civilized zones, the sahuagin use them much as humans use hounds. Dragon turtles serve different roles depending where they’re found; in the Dominion, dragon turtles are forced to serve as beasts of burden and living engines of war, while the merfolk form alliances with dragon turtles and consider them partners in a community.
Later sections explore the relationships between the major cultures of the Thunder Sea. Here’s general information about other sentient aquatic creatures in the region:
Locathah are subjects of both the Valraean Protectorate and the eastern regions of the Eternal Dominion. The locathah never had a civilization as advanced as the sahuagin, and have been subjects of the Dominion for thousands of years. However, there could be bands of free locathah on the edges of the Dominion, potentially hiding in the territorial waters of Khorvaire.
Storm giants once had a presence along the coastline of Xen’drik. After devastating conflicts with several sahuagin nations, they were all but wiped out. Today, they’re generally known only through the ruins and tombs they left behind, usually protected by powerful magic and left alone by the Eternal Dominion. There are still a few storm giants in hiding; most are shadows of their former glory, but there may still be a few hidden giants who have preserved their ancient powers.
Dragons have much the same relationship with the Thunder Sea that they have with Khorvaire. There are a few rogue dragons (black, bronze, green, or gold) who pursue their personal goals in isolated regions of the Thunder Sea. Elsewhere, the Chamber monitors the Dominion just as it watches humanity, intervening only if its interests are threatened.
Kuo-toa have no significant presence in the Thunder Sea, though they are found elsewhere in Eberron.
Koalinth were developed by the goblinoid Empire of Dhakaan to defend the coastline, though the dar never sought to cross the sea. These aquatic hobgoblins were exterminated by the sahuagin following the collapse of the empire, though koalinth tribes are occasionally discovered in remote locations. It’s possible a more sophisticated clan of koalinth went into deep seclusion at the same time as other Kech Dhakaan; if so, this could be an interesting ally for the Heirs of Dhakaan.

Kar’lassa, Dar, Kalashtar, and Elves

When the dar dream, they are drawn to the Uul Dhakaan, the shared dream of the empire—but when anyone dreams within 13 miles of a kar’lassa, they’re drawn into its dream. So what happens if a golin’dar dreams near a kar’lassa? These ancient primordial forces trump the work of Jhazaal Dhakaan, and the dar are pulled into the dream of the kar’lassa instead of to Dal Quor. However, all of the dream-tools crafted by the Kech Dhakaan—the kra’uul and uul’kur— function normally within the dream of a kar’lassa.
What about kalashtar? Their connection to Dal Quor has been completely severed, but they do dream; when a kalashtar sleeps, they create dreams within their own mind, drawing on their memories and their quori spirit. However, if kalashtar find themselves within the range of a kar’lassa, they’re pulled into its dream, as with the dar.
The sea elves of the Valraean Protectorate are aware of how the kar’lassa influence the dreams of “lesser” races. Though the Protectorate hasn’t yet captured any Dominion cities, they take great pride in their belief that because they don’t sleep, they would be above the influence of the kar’lassa—but this belief is wrong! It’s true that elves trance rather than sleep, entering a deep meditative state much like a lucid dream, self-directed and untouched by the influence of either Dal Quor or a kalashtar’s quori spirit. However, this process is physiologically similar to a human’s dreams and can likewise be hijacked by the kar’lassa—which would be a startling experience for an elf who’s never dreamed before!

Type

Sea

Krakens

The Thunder Sea is home to the ancient evil of the aboleths, who yearn to dominate the minds of all creatures. It holds the sleeping kar’lassa, who could devastate cities or nations if they rose from slumber. Where do the krakens fit in this hierarchy?
Krakens are children of Khyber, born in the Age of Demons. Unlike the aboleths, they weren’t created by a fiendish overlord and they don’t serve any overlord; each kraken is a power in its own right. Krakens enjoy exercising their power and being worshipped by lesser creatures, and each one carved out a domain within the chaos of the Age of Demons. The binding of the overlords didn’t adversely affect the krakens; however, many feared that the alliance that had formed to defeat the fiends might well turn its attention to them next, so they chose to go into hiding and sleep, waiting for an age when the champions of the Age of Demons were dead and the oceans were free.
Krakens are spread across all of the oceans of Khorvaire. For the most part, they don’t work together, in part to avoid the interest of Argonnessen. One kraken dominating an island of humanoids is of no concern to the dragons; an alliance of krakens is another story. However, multiple krakens have occasionally joined forces. Tens of thousands of years ago, five krakens devastated the previous civilization of the sahuagin of the Thunder Sea. Despite their power, they were eventually overcome; their remains are preserved in the city of Hal’shavar.
There are a few krakens in the Thunder Sea, but they avoid the Eternal Dominion, dwelling either in its fringes or in dangerous places that are shunned by the sahuagin. The kraken Bastyreth has established a sanctum below the kar’lassa tied to Mabar; it’s raising a legion of undead minions and preparing to take vengeance on the Dominion.