|Region||Troll Bogs, Slilp-Urp|
Along the southwestern coasts of the Troll Bogs is a vast network of sea caves and Underdark passages called Tûnin-Gil. The caves are at sea-level and partially submerged in the waters of the Pearl Sea. The caves then go northerly through old lava tubes. After some distance, this area becomes part of the Underdark region Slilp-Urp. For miles into the caves, areas are often lit by open air shafts from long dead volcanoes and there innumerable sink-holes and vents. An enormous quantity of water falls into the caves from the swampy lands above. This wetness and light from the holes leads to massive fungi growths on the ceilings and vast clumps of floating vegetation.
Several of the sea entrances are large enough to accommodate ships. In the Third Epoch, realms of the surface began setting up trade routes with some of Slilp-Urp's civilizations. With the trade, came Underdark pirating and the usual conflicts over who owns the sea lanes. In addition to the threat of pirates, Tûnin-Gil is haven to numerous gargoyles, harpies, and stirges. These creatures roost in the countless sink-holes, chutes, and crevices from the Underdark sea passages to the surface.
Ten miles into the sea caves is a mammoth passage leading to Nagdúrzol and the Spire of Rioch Tetrax. In the Horgon Era, these two areas were ruled by the Durkoth. Tûnin-Gil's waterways served as highway to reach potential new subjects. When the Durkoth left for the depths of the seas, their former minions, mostly Dromites and the Laupha, were left to their own designs. The Laupha, bitter with being kept in the tight environment of Tûnin-Gil and in the Underdark for so long, were the first to leave the area. Half of the area's Dromites would followed suit, heading for the islands of the Buccaneer Archipelago and the Pearl Sea.
... a hundred feet or more of this Helas Vessel lies submerged in the dark sea.
- excerpt from the book "The Horgon Spires of Midrêth"