Death's Manor was seen in "Dead at Eight". It is the place where Death, Death's Wife, and Thomas live. Death invited Mordecai and Rigby there to babysit Thomas while he and his wife go out for dinner. The interior of the manor is wrecked at the end of the episode.
Death's Manor is a daunting-like, iconic manor with very dreading designs. Once one enters the manor, there are two staircases and a chandelier in the middle. There are many rooms, like the library, Thomas' room, and the kitchen. The exterior is both dark and light grey with trees surrounding the mansion.