The Rift

Northeast of the Capital island of the Reman Empire is a phenomenon unique in the world. A whirling maelstrom of waves and magic endlessly drawing downwards to the deep ocean floor below. Legend claims this storm is the remnants of the Storm of Wrath when the Children fought so viciously they shattered the west, creating the Reman Islands. In this legend, when Krumas and his allies were defeated the storm that broke the land continued to hammer down on the throne of the hunter, driving it deep into the sea floor and continually buffeting it with the waters and combined rage of Upe, Aurou, and Rugiai. While this makes the throne all but completely unapproachable it is said the force of this storm is so great that it pierces the world sending water bursting into Tyn below.
This malefic whirlpool is known by many names colloquially, but is most commonly called "the rift," the namesake of the small city of Riftport. It lies at the center of the shard islands just off the coast of Rema Prime. The town of Valencia lies on an island to the west of the rift and mostly survives on the traffic of tourists and pilgrims visiting the rift. Despite the ferocity of the storm itself, the islands nearby do see to go about a normal life. 
Below the waters, the Adventi consider the rift to be a holy place, a relic of the Precursor and origin of their civilization. In the marine realm the effects of the maelstrom are more pervasive, with powerful currents and odd temperature changes reaching out miles beyond the nearest few islands. While these effects worsen the closer to the throne one moves, likely making even trying to reach it fatal, the Adventi maintain a guard here to ensure that no mortal, Adventi or otherwise, makes the attempt. While this cumulative opposition would dissuade nearly anyone, there are stories of mortals who've reached the throne and used it as a path to enter Tyn, though why any would seek such a thing is unknown.