Described herein is a walker for moving a structure over the ground. The structure to be moved may be an oil and gas rig for instance. The walker includes a pontoon for engaging the ground, a jack with rollers disposed on the pontoon for lifting the structure and sitting on rollers, a longitudinal drive assembly for longitudinally moving the pontoon relative to the jack with or without the structure on the rollers, and lateral and rotational drive assemblies for moving the jack and the pontoon relative to the structure when the structure sits on the ground.