Conventicle of the Dead

The Chapel of the Dead is a holy place dedicated to Lithos. It is here, where Lithos buried the Heart of Earth, guarded by his undead servants. The Chapel lies deep in the Catacombs, in the Pit of Death, and the only woman who has a key is long dead, buried in the Pit. Thus the Chapel stays locked.

However, the Avatar nonetheless managed to enter the Chapel, and take the Heart of Earth from it.

Trivia

 * There are actually two way to enter the Chapel. Either find the key, or use a golem, even if it can't reach the doors, it will open them.