| Category | Caverns |
| Continent | Brucrumus |
| Region | Phangul |
| Map | Sygning |
Hlat'tar is a massive cavern of Sygning. In the early years of the First Epoch, this cavern contained a deep lake that was home to the aboleth. Subjected to slaving, raids, and outright war, the drow of Filion'lyr hatched a bold plan. They constructed a lock system that over two decades drained the lake, leaving two aboleth city-states exposed to naval bombardment and easier access. Besieged, the drow then poisoned and fouled the shallow lakes around the enemy's partially submerged cities. The drow did not relent, with the last of Hlat'tar's aboleth eliminated on 19 Hollow 261.
The River of Vuzlyn carves through Hlat'tar. When the Filion'lyr opened The Mandible, draining the lake, this river forged a new course. The significantly lowered water level left behind numerous pools, wetlands, and two small lakes surrounding the ruins of Azoloch and Gon'tora. Hlat'tar is a verdant, subterranean landscape teeming with lush plant life and unique lifeforms, with continuous dripping from above creating a perpetually damp environment. In the south, near the city of Filion'lyr, vast farmlands are tended by Myconid and their drow overseers.
Along the northwestern stretch of the Great Tradeway, the predominant mode of transportation is waterborne, with vessels conveying goods and passengers through the region. This approach enables avoidance of the numerous shambling mounds, oozes, and the occasional undead aboleth that inhabit the area.