The Object Locative Environment Coordinate System is an engine that determines and calculates a robot's interaction with the environment based on the camera's current perspective. Gaps can disappear behind a pillar, bridges can be joined just by rotating the camera, and all sorts of weird mind tricks can be accomplished with a little experimentation or plenty of imagination.
Save a layout with F3, and load a previous one with F2. It saves to the ole.dat file, and it seems you can only have one at a time. There's a pretty complex world as the default, so back it up before you make new levels.