Tower of Gaan-Telet
Gaan-Talet is a difficult, multi-layered dungeon. Like Halls of Steel, there is a Hard and Vicious difficulty available. Hard is unlocked by collecting at least one of every monster trophy at the Taxidermist. Vicious (often considered to be the most difficult dungeon in the game) is unlocked by completing the quest to defeat Hard with the Purist badge.
The exterior of Gaan-Talet contains the shops, glyphs, and boosters of a normal dungeon. There are no altars (on the outside), and there is no normal subdungeon, although the Smuggler's Den will appear if you prep it. Ordinary monsters from level 1-7 appear on the outside; there are no level 8+ monsters or bosses on the outside. The inside of the tower begins revealed.
To complete Gaan-Talet, you must enter a series of special subdungeons inside the tower. Once all enemies in each level are defeated, the next becomes available.