Diabolic Hall (Death Palace originally) is a demon fortress in the human world in Dragon Quest IV. Located to the east of Riverton, it is a common congregation spot for expatriate demons. It also serves as a prison for various humans captured by the forces of Hell.
The party visits Death Palace fairly late in the game, infiltrating its walls using the Mod Rod to take on the appearance of monsters; they can only properly interact with the inhabitants while in monstrous form, as speaking to one while in any other guise triggers a battle. After progressing to the inner hall, the party witnesses Psaro's address to all demons, which is actually the first time most of them see him in person. Psaro gets his point across, but before he can wrap up the meeting, he receives a report that the humans at Mamon Mine have accidentally excavated Estark's tomb and that he will soon awaken; as chaos breaks out, he takes off to react to this latest development, and the party makes good its escape to confront Estark.