Cocytus

A-113 is a small space station dating to the Golden Age in stationary orbit above Ceres. The station's purpose is unknown, as any records of its existence did not survive the Collapse, but it contains "keyholes" that seemingly lead to other dimensions that drive those who enter them to madness or worse. The station was rediscovered by Dead Orbit, who gave it its current designation and kept it a secret from the Tower. A subsequent expedition there ended in failure: an Awoken ship from the Reef crippled the expedition's ship, the Sophia, and exploration of A-113 rendered most of the crew insane. The crew's Arach found a dead Ghost on the station and sent it back to the City with a request that Dead Orbit strike A-113 and the expedition from their records.

Trivia
A113 (sometimes A-113 or A1-13) is an inside joke, an Easter egg in works created by alumni of the California Institute of the Arts, referring to the classroom used by graphic design and character animation students.