The Abyss

The Infinite Layers of the Abyss, sometimes known as Demonholde, is the home plane of demons and is known for being infinite in size and depth. Found between the windswept plane of Pandemonium and the prison plane of Carceri, this plane is considered to be mildly evil and mildly chaotic, though that doesn’t mean it’s safe by any stretch of the imagination. The demons and other evil creatures who roam these layers see the only way to gain more power is to enforce their will over others, be it by enslaving them to the demon armies in the Blood War or to use violence to impose their will.
The plane itself shares many of the same traits as demons, though it acts in a far more devious manner. Littering the top layer of the plane are conduits that lead to almost every layer in the Abyss, though few are marked and even fewer are reliable. Some layers might only have one-way portals and be impossible to escape until someone, typically a powerful abyssal lord, releases you or the conduit might take you to a world that appears to be The Material Plane except that the plants feed off of blood instead of sunlight. Due to the assumed infinite number of layers on this plane, it can be difficult to know exactly where you are when you take a conduit, though several layers have been ‘civilized’ by the demons and actively encourage, and protect, traders to their cities.

Geography

Decay, corruption, and entropy are all that await visitors to this plane of chaos and evil. Most who journey to this plane never get further down than the first layer, known as the Plain of Infinite Portals or sometimes as Pazunia, so named for the great demon lord Pazuzu who can often be found on this layer. The plane is brutal and outsiders who arrive here must learn quickly to think on their feet to ensure they don’t become pressed into the Blood War effort or killed by a bored demon. Portals that lead out of here are often guarded by demons who are tasked with gathering up fresh recruits for the demon armies, though they can be bribed with magic items, jewels, and similar goods, except for gold coins as the demons place little value on a metal they deem largely worthless. Power can only be won through strength and violence.
Manual of the Planes, 2008 WotC Manual of the Planes, 2008 WotC
Those who choose to travel to the Abyss should be ready for a torturous experience and be well prepared for a fight. Those who can subjugate others can quickly gain a large following of demons, mercenaries, and more on this plane, though they should always remember that the Abyssal lords, also known as the demon princes, rarely take kindly to their subjects being taken away from them. Any time one person gains power, someone else loses it and the most powerful on this plane despise ever losing anything.
If a traveler hopes to survive the plane, and explore more than just a single layer, they will have to use the conduits that link all the layers with each other. Spread out are an infinite number of portals on the first layer, all leading to different layers on this plane, though few are marked as to where they go and even fewer are accurately marked. Those who venture into these layers rarely come back out, and of those who come back out, only a handful can escape with their mind intact. The Abyss is devious when it comes to how it affects its inhabitants, infecting their minds with a madness that refuses to ever heal.

Ecosystem

Known as the home plane of demons, the Abyss is a chaotic evil plane built on the assumption that might makes right. While demons largely rule most of the known layers, other creatures, all evil and chaotic in nature, can be found in many of the layers, these creatures include undead, bodaks, renegade Devils, corrupted mortals, and more. While the demon princes are considered to be the rulers of this plane, many of them are simply just powerful demons instead of powerful deities. Because power is all about your dominion over others, those demons who prove themselves to be the mightiest of their kind can often find themselves ruling sections of a layer, or an entire layer if they can just get others to fall in beneath them.
Life on this plane is hard and brutal, those who lack power are abused by those with power. Those with power are paranoid that their power could be taken away from them, and those who scheme for more power are often killed brutally and painfully to show others what happens if you go against your betters. Those who rise must always be on guard, for there is always one more powerful than yourself, and knowing when to push your muscle and when to prostrate yourself are important life lessons that few get to survive after a single mistake.
Beyond the constant power struggle of the demons and other natives of this plane, the inhabitants must also fight against the plane itself. Some layers are blistering hot or freezing cold, others are bogs of acid, deserts of crushed bone, or near-perfect copies of The Material Plane. Every layer is different, and all of it is devious. What might appear at first glance as a normal field of grass could easily become a field of carnivorous plants that feed on flesh, bones, and blood.
Plane of Chaos, 1994 TSR Inc. Plane of Chaos, 1994 TSR Inc.
Despite the dangerous nature of this plane and its inhabitants, it isn’t all terrible. Some powerful lords have gotten it into their heads to make their domains proper cities and trading outposts, all to gain more power over others through magic items, wealth, and more. These cities often have very few rules, as it isn’t in the Abyss to follow law and order, though traders are often highly protected by the demon lords, for if the traders are too fearful to come, their dreams and aspirations of becoming a powerful city ends. Many times a trader will be given several strong demons to act as their guards, ensuring that a trader can come and go from the Abyss unmolested, then again, sometimes demon princes can change their mind and take what they want from a trader and leave them stranded on a layer. It’s difficult to stick to long term plans on this plane as sudden emotions and passions can overwhelm even the strongest willed.
Atmosphere The Abyss’ atmosphere is largely dependent on which layer you are on, and how that layer functions. On the top layer, the Plain of Infinite Portals, it is hot with a fat reddish-dim sun that burns away any vegetation that tries to grow on the layer. On another layer, the air might be laced with poison or disease, while another layer could have no atmosphere or be completely unbreathable for a mortal being, or the layer could be hundreds of miles of ocean with no sight of a surface.
Despite the six hundred plus known layers of this plane, only about a fifth of the layers can support life for the typical traveler. Luckily, most layers have their own source of light, it could be harsh red light from a burning sun high above, the ground might emit greenish light that casts shadows high onto the clouds above, or the light could come from good-aligned creatures who shine like beacons, the more good a creature, the brighter they shine. There are a few layers that are pitch black and even some that act more like a vacuum, feeding off the light and extinguishing it before you can see the world around you.

Localized Phenomena

Magic and the Abyssal Lords Spellcasters are, by and large, mistrusted by demons and the other inhabitants, and for good reason. Those who practice magic often lack in a powerful appearance, leading many demons to assume that spellcasters are weaklings, just waiting to be subjugated under a powerful creature. For those, it’s often the last mistake they will ever make, and for the spellcaster, casting any spell immediately puts a target on them. Demons hate spellcasters above all else because of their rituals of binding and summoning, dragging them out of the Abyss, and into another plane where they are placed under the control of the summoner. No demon wants to be beholden to another creature, especially one who it thinks it is more powerful than.
Plane of Chaos, 1994 TSR Inc. Plane of Chaos, 1994 TSR Inc.
Those who cast spells while in the Abyss should be mindful of where they do it, and in whose domain they do it in. Spells immediately attract the attention of whoever controls the domain, bringing unwanted attention to any travelers trying to sneak their way through the territory. Some types of spells are more likely to anger a demon prince while others may be completely ignored, it all depends on who it affects and how. A spell that only affects you or your party can be ignored, while a spell that damages another demon might be met with a team of demons sent to capture you for the Blood War. If a spell is used to control a demon or force them to follow your commands, this calls for immediate and severe action by whoever holds power in this domain, and a swift and bloody end to the spellcaster.
Rumor has it that a demon prince always knows when a spell is cast in their domain, allowing them to easily hunt down spellcasters. Spellcasters should always be cautious about how and what spells they cast, especially if they are planning to sneak in or mind control one of the inhabitants.

Natural Resources

The Plains of Infinite Portals This is the top layer of the plane and the most traveled too. It’s one of the few layers that are survivable, at least as far as the environment is concerned. The dim light of this plane is provided by the bloated red sun that burns away anything that would try to grow here. Large pits dot the dusty and barren landscape, these pits are the conduits that lead to the other layers of the Abyss, though few of them are marked. Massive fortresses made of iron are the strongholds of the Abyssal lords, each of these fortresses are filled with devoted servants who protect their lord’s body while the powerful demon visits the other worlds as a spirit, seeking to corrupt and spread their brand of evil.
Portals lead in and out from this layer with very few touching on the lower layers, typically when a portal does reach a lower layer, it is only due to bad things. A demon somehow found a way to open a portal your Material Plane, a summoner foolishly didn’t close their summoning gate correctly or the cultists have finished their rituals and a demon army descends upon an unsuspecting world. Some say that the Abyss is made up of ancient worlds that the demons conquered, that once they completely corrupt the land, it can fuse with their plane and becomes yet another layer.
Demonomicon, 2010 WotC Demonomicon, 2010 WotC
There are several important sites on the Plain of Infinite Portals like the Lakes of Molten Iron, massive crucibles filled with white-hot and red-hot molten material for use in the construction of the iron fortresses and the weapons used in the Blood War. The River Styx flows through this top layer, it’s waters trickle past the town of Styros, a barracks-town overflowing with thousands of demons waiting to get shipped off to do their part in the Blood War. The molydeus, powerful demons who only answer to the strongest of the Demon Princes, send these hordes off in rickety and questionable boats. Sometimes as much as half the forces sent will sink on the journey there, the molydeus see it as an acceptable level of casualties and keep sending more.

Tourism

Travel to the Plane Most who travel to this plane rarely make it back, those that do are often forever changed by their experience. Those who wish to travel to this plane are strongly encouraged to not do it, that whatever they are searching for is not worth the price of coming to this plane, but people still come. To get to this plane, one can find portals from all over leading to the top layer, the Plain of Infinite Portals, though there are a few portals that will take you to a different layer.
The portals in the Astral Plane take on the purple color of amethyst, and the two neighboring planes, Pandemonium and Carceri, feature portals to this plane. Portals in the Abyss take on the form of pits, sometimes they appear to be bottomless, sometimes they have a bottom, and sometimes they aren’t portals and are just dangerous pits that clueless travelers step into and plummet to their death.
Once you arrive on this plane, it is far harder to leave as the demons and other inhabitants don’t like outsiders coming and going as they please. Powerful demons guard the portals out of this plane and ensure that anyone who arrives here learns their proper place.
Traversing the Plane Manual of the Planes, 2001 WotC Manual of the Planes, 2001 WotC
Depending on which layer you are on, traversing this plane can be very easy, very dangerous or you can immediately perish. Some layers are completely unknown and could be a perfect representation of The Material Plane, while other layers could just be copies of the Plane of Fire or the Plane of Water. Much like how Limbo is chaotic, so are the layers of the Abyss, though their big difference is that the Abyss isn’t constantly morphing and changing. A layer rarely changes itself unless there is a suitably powerful individual to morph it to their will.
Some demons gain enough power to do so, but most are unable to, the ability to morph a layer or at least part of it, is largely reserved to the most powerful demon princes. Of the princes that can morph the Abyss, most can only adjust a small portion of the layer, but the more powerful you become, and the more worship you can accrue from those in The Material Plane, the more you can morph and control. One prince, Graz'zt, lays claim to three layers that are interconnected, while another prince, Lolth, only claims two layers.
Some layers could never be controlled by even the Gods simply because there is nothing to work with or it’s a trap layer. Trap layers are typically devoid of anything, including portals to leave the layer, and you are simply floating through it until someone powerful enough can release you from the outside, or some layers only require another creature to show up and you are then shunted out of the layer as someone else becomes trapped. Another layer could be so completely full of demons that there is no land due to the miles and miles deep pile of demon bodies that cover it, all attempting to climb above the others so that they can gasp for breathe through the press of bodies.

Type

Plane of Existence

Location under

Lower Planes