When viewed from below, a user’s feet cast shadows onto the floor screen of an under-floor projection system, such as the six-sided DiVE. Tracking those shadows with a camera provides enough information for calculating a user’s foot location, orientation, and movement. Shadow Walking affords virtual locomotion by detecting if a user is walking in place, their direction, and step speed. This technique also gives the programmer the opportunity to use user foot movements as triggers to make things happen, without cumbersome sensors. Shadow Walking provides advantages of being unencumbered, inexpensive, and easy to implement compared to other walking-in-place approaches. It also has potential for extended gestures and multi-user locomotion.