The Cantina, seen here in the top left of Mos Eisley, is based on a couple of designs that I saw on the internet. It has a main room with the bar, and then rooms of to each side, as well as an entrance chamber.
Filled with all sorts of Alien life, scoundrels and bounty-hunters, it is the central gathering point in town. The Cantina band plays whilst all sorts of shady deals take place.
The whole roof lifts off in several sections in order to facilitate easy play.
This was the first builing to be constructed, and has remained largely unmodified as the rest of Mos Eisley has grown up around it.