
Petra is on your top priority list if you are in Jordan. Located in the Wadi Musa Canyon the solid red sandstone buildings, carved by the Nabataeans are unlike anything you have ever seen.
The Siq, a narrow gorge leads you to the temples, tombs and other buildings. While you are walking through The Siq (you can also rent a donkey) you never expect what is coming. Then you take a trun and 'bang' it's there: the most impressive red sandstone temple you have ever seen. It's so big you can never take a good picture of it. The best way to appreciate it is to see it in reality anyway.
After this first shock, there is a big area with many similar temples, tombs and other magnificent constructions. you need a full day to see everything.
The best way to visit is by foot. You do need lots of water and you should protect yourself against the sun. We're in the middle of the desert, you know.
Petra is less than 200 km south of Amman. You can visit Petra as a daytrip, but you are sure to miss a lot of things. It is also possible to see Petra on the way from Amman to Aqaba. A visit to Petra can (and should) be combined with a stay in Wadi rum. That's the way to fully appreciate the beauty of the desert.
(It would be nice if this included information on how to reach Petra, and nearby hotels/hostels for travellers.)