If you have, then you've probably been to a liminal space. On the Internet, that usually refers to empty rooms, corridors, ...

The scenes they contain are ordinary: a corridor of unmarked doors stretching into blackness; a slide leading to an empty, windowless ball pit; an indoor pool illuminated by an unearthly glow.

Perhaps the Internet's most notorious liminal-space experiment ... large rectangular indoor pillars-- these elements are combined with sterile, modern spaces, like corporate offices, school ...