Here is yet another test for fold-flat terrain, in this case dungeons or sci-fi bases. The wall segments are simple two-sided strips with a folded base to hold the floor piece. Walls are conected by triangular posts, with small paper clips (in this 15mm scale version).
This is what the pieces look when taken apart:
Multiple rooms can be connected simply by adding more posts and walls. The main problem is finding a better way to fix the floor. Currently, it is held between the triangular posts and the folded pieces of the walls, but this is not very stable.
One alternative might be to simply have a large floor tile and place the entire set of walls above it, instead of having separate floor pieces for each room.