| Category | Subterranean |
| Continent | Karterus |
| Region | Dhark Bolg |
| Map | Tiyaphis |
A large area of Tiyaphis is composed of old and active lava tubes. Majority of these are defunct tubes that function as natural corridors for the creatures inhabiting the Underdark. This region is known as Sephu'phis, named by the ruler of Varelay after a maralith who served as a guard captain and concubine of the demon emperor Aperoq. The flow of lava through the area was significantly altered during the Varelay Upheaval (2608 LE - 16 HE), leading to numerous lava tubes becoming inactive or defunct.
The central lava river, the wellspring of magma for Hen'khas's volcanoes, meanders through the core of this region. In recent memory, it has become known by a term in the Giant tongue signifying Surturs Eyebrow.
Sephu'phis is a labyrinth of lava tubes, some active and others dormant. The active passages lead to lakes of molten rock or fungi-thriving forests near the heart of the region. According to the local inhabitants, no one has navigated even a fraction of the tunnels.
In the southernmost regions lies the venerable city-state of Aebilchunus. The illithids of this venerable metropolis dispute the territorial assertions of Goth-Dyvermoir over portions of this domain.