Visitor Centre More of a warden's post than a visitor centre, there are at least toilets at the entrance to Umm Al Jimal. For more details about the site, look for the hard-to-find booklet Umm el-Jimal (JD3), published by Al Kutba and available sporadically at bookshops in Amman.
Archaeological Office If someone hears your arrival, you'll be expected to sign the visitors' book. So few visitors come this way, however, you can excuse the warden for wandering off post now and again. While it is tempting to slip into the site incognito, it's probably worth letting someone in this office know that you have stepped into the site, just in case you break an ankle walking over the rubble. The site is so big and so deserted, you might not be discovered for days!
Department of Antiquities This is the place to address any technical queries about the ruins, although the office is often closed.