The Cube

A sealed cube of rooms joined only by vents. The room you step into is green - you're safe. But linger and it fades white, bakes orange, then burns red as the Cube purges you to death. Walk through an open vent to travel - and the vent stays open behind you, so you can come back the way you came any time you like. Edge vents open onto open space - step off the Cube and you are lost, unless you reach the bridge and walk out to win. Multiplayer: everyone shares the same cube - first one through the bridge vent