Room-over-room

Room-over-room is a term used to describe placing a room directly above another, often used in reference to id Software's Doom series, which didn't allow for it. In the original Doom games, all mapping was done in 2D, while height variance was done via numbers. In true 3D engines to follow, such as the Quake engine, this proved an easy effect to pull off.

The restriction was originally subverted by using a silent transport to give the impression of seamless travel between two stacked rooms, but has since been completely corrected in some source ports, such as Doom Legacy. In game engines such as Cube, room-over-room can be mimicked using 3D models.