One of the first and most popular demos for the Oculus Rift was the Rift Coaster. A simulation of a roller coaster bound to tracks (much of the time) with a well illustrated environment which helped immersed the user.
Check out the video above for some funny reactions. This clearly illustrates the power of virtual reality and how it can change your perception of an environment. It can even trick the brain in to the feeling of motion, even though you aren't going anywhere.