Entropis

Entropis is a tower at the center of Thar Amphala. Vox Machina encountered Vecna, the Whispered One, for the first time at the top of this tower.

Description
The tower is described as an "ominous, commanding, massive spire of obsidian black... A jagged monolith that exudes ancient hatred, encircled by dozens of dark, winged beasts that watch over the dreary skies."