The Fathomless Spire is a tower in the Crown District of Earion, and is home to the Earion chapter of The Arcane Institute. The spire is constructed of obsidian and seems to absorb the light around it. It's positioned in a way that allows it to overlook much of the city.

The spire is mostly a place of learning, but the chambers of the chapter's leadership can be found on the upper floors.