Prince of Persia

There are some chompers in the game which retract into floors with no walls beyond them to cover the blades.
For example, the chompers on level 5, in the room where the shadow steals the potion.

Some spikes and gates do this as well, but they tend to be on the edges between rooms, where this is less visible.
For example, when the gate on level 12 opens, it should logically appear in the room above.

There is an old video about the development of PoP which shows that opening gates used to appear in the space above them.

Funnily enough, one "row" on top of the gate simply vanishes before the rest of it starts to appear above it.