Abstract: An expandable retract able portable structure is provided having a stationary portion and a movable portion. The movable portion pivotally encloses the stationary portion in the retracted configuration. A hydraulic, pneumatic or gear driven actuator carried by the floor of the stationary portion co-operates with a linkage mechanism to rotate the movable portion through approximately 90.degree. to the expanded position. The roof of the movable portion is hingedly connected to one wall. The unit expands or retracts in one single pivoting motion through approximately 90.degree..