Obsidian Cathedral
Where the lava tunnels converge sits a vast chamber made entirely of black glass. Formed from a massive magma bubble in past aeons, the Obsidian Cathedral holds the curious property of muting all light within it, and its ice smooth floors require great care to walk upon.
Large, rectangular blocks of black stone, carried by a river long since gone, litter the floor, vaguely resembling pews in uneven rows. In the exact center of the room sits a perfect cube of polished obsidian with a shallow basin atop it, though there is no sign of how it got there.
