It's a problem that has long annoyed virtual reality researchers: VR systems can create a good experience when users are observing or manipulating the virtual world (think Michael Douglas in "Disclosure") but walking is another story. Take a stroll in a virtual space and you might end up with your face against a real-world wall.
The same problem is becoming apparent in teleoperated robots. Imagine you were teleoperating a humanoid robot by wearing a sensor suit that captures all your body movements. You want to make the robot walk across a room at the remote location -- but the room you're in is much smaller. Hmm.
Researches have built a variety of contraptions to deal with the problem. Like a huge hamster ball for people, for example.
Or a giant treadmill. The CyberWalk platform is a large-size 2D omni-directional platform that allows unconstrained locomotion, adjusting its speed and direction to keep the user always close to the center. With a side of 5 meters, it's the largest VR platform in the world.