Named for its purplish tint, the Heliotrope Sea is in the subterranean region Phangul. Its color comes from the stone Dušullu-Ošur, bleeding into the waters around it. This stone is shipped on great barges to Phure-Zil then upwards by ramps and elevators to her sister city on the surface. From there it heads south, becoming construction materials for holy places. In addition to blocks of Dušullu-Ošur, a great variety of trades passes across a sea area serving as the heart of the Gnemdos Trade Network. The core routes of this trade network extending outward in all directions are the ports of Snahyrull, Dienkigec, Phure-Zil and up the river Belevorn to Gnemdos.
From the north, this sea is fed by the Belevorn River. From the surface, thousands of feet above, three great waterfalls and many smaller empty into this sea. The journey begins in Pellangoth's forest floor, three mammoth holes, big enough that a dragon with wings outstretched could fly down them.
The largest outflow of the Heliotrope is the southwest flowing Nedullu. This river will take a traveler all the way to the Ebonmurk; another Underdark sea hundreds of miles to the south. The Gaereaus traverse this distance on massive steam-driven barges, carrying their wares to the markets of both Underdark and surface civilizations.