I know someone linked to the indy FX but I'll post them here so you don't have to search around those threads. I'll try to make it as clear as possible.
The three rooms are really all the same room. There are actually 5 doors,1 is real and the other 4 are painted on but only three can be seen at once. The walls on either side of you move so if they move all the way to the left then the door on your far right is the real one. If the walls are in the middle then you go through the center door. and if the walls are all the way to the right then the left door is the real one. They just change the FX, lighting, and scrims inside the room to make them look different.
The boulder is a large ball that just sits stationary while spinning on an axis. Your EMV stops and the hydraulics move around, during this time EVERYTHING in the room including indy on the rope, except you and the boulder begin moving forwards. This gives the effect that you are moving backwords, sort of like when you are at a stop light and the car next to you moves a little. Naturally if you moving back the boulder should be getting further from you, but since it doesn't your mind feels it is getting closer, plus, it seems to get closer to the walls in front of you since they are moving towords it. The strobe completes the effect and you speed down ahead.