One of the joys of visiting Umm ar-Rasas is the lack of other people. These extensive ruins may be home to some of Jordan's most magnificently preserved mosaics, but there's hardly ever another visitor in sight.
The main focus is St Stephen's Church, with its incredibly impressive mosaics, protected from the weather under a large metal hangar. If you don't have much time, concentrate your visit here viewing the intricate mosaic panels which depict the important towns of the Byzantine era—including Madaba and Jerusalem—as well as vibrant pictures of everyday life.
If you do have time, though, the slumping ruins of Kastron Mefaa (once the main settlement here) are fun to explore. Scramble over the fortifications and pick your way through collapsed arches and rubble to find the remnants of churches with scraps of mosaic detail still decorating the floors.