About 20km south of Amman, right beside the main international airport, is Qasr Mshatta, one of the biggest of the desert palaces. Although there are various theories as to its date and purpose, Cresswell argues convincingly that it was probably built around 743AD by the Umayyad Caliph Walid II and that it remained unfinished after his death.
Only the northern half of the central third of the palace was ever completed; the photo shows the view of these buildings from the centre of the enclosure. In the middle was a triple-apsed building with massive square piers which presumably formed the throne room/audience chamber. Either side are symmetrical arrangements of rectangular tunnel-vaulted rooms.
Despite its importance and its proximity to Amman, the ruins at Mshatta are remarkably peaceful. Getting to the site requires a bit of effort as it's in a restricted area within the airport security zone. You'll need to leave passports at a military checkpoint but they're quite friendly about it. The caretaker lives alongside the site and will almost certainly offer you tea (which he flavours with wild sage - a delicious concoction!) When I was there, he hadn't had any visitors for about two weeks and seemed delighted to have some company.