These massive multistoried vehicles are used by jawas on Tatooine. The jawas live, work, and travel in them. They are about 70 feet tall and can hold 300 of the diminutive scavengers. Sandcrawlers have 8 caterpillar treads powered by fusion reactor engines.
Riding in these mobile cities, jawas roam the desert looking for discarded machinery and junk. In this way, R2-D2 and C-3PO were picked up and later sold to Luke Skywalker's uncle.