Caves of Koilos

The Caves of Koilos were a network of tunnels in the Koilos region of Terisiare, hidden away underneath the Kher Ridges. They were amongst the few intact remains of the Thran Empire and held an impressive array of ancient Thran artifacts that were excavated by the Brothers during their apprenticeship to Tocasia. The caves were also the site of the only permanent portal between Dominaria and Phyrexia, making the desert around them an important battleground during the Phyrexian Invasion.

During the time of the Thran Empire, the caves were home to the Untouchables, people from the underclass of Thran society that had been infected with phthisis due to too much exposure to powerstones through working in the Mana Rig. Because of this, the caves were known at the time as the Caves of the Damned. The permanent gate to Phyrexia was created inside the caves during this period so that Yawgmoth could transfer the Untouchables to his plane, under the pretext of curing them. In fact, the Untouchables were turned into Yawgmoth's first Phyrexian warriors.