Irrat is a small cavern adjacent to the main D'ni Cavern where the Guild of Maintainers operated a prison stronghold. It is one of the caverns of D'ni in which there was a lake and at least 1 island.
Upon arriving in D'ni from the surface, Ti'ana was taken to Irrat until the Guild Council decided what would be done with her. While there, she was interrogated by the Guild of Linguists, and taught to speak D'ni.
Veovis was also imprisoned in Irrat while awaiting his trial for the murder of 2 guildsmen and the trade of illicit Ages.