Apodyterium

An apodyterium was a room in Caesar Nero's palace. In July 64, the First Doctor and Vicki entered the room after Tavius suggested they visit — only to discover there the body of the centurion who had escorted them to the palace. (TV: "All Roads Lead to Rome")

Behind the scenes
The Romans never properly defines what an apodyterium is. In the real world, it was a room for disrobing.