From the World Heritage inscription:
Inhabited since prehistoric times, this Nabataean caravan-city, situated between the Red Sea and the Dead Sea, was an important crossroads between Arabia, Egypt and Syria-Phoenicia. Petra is half-built, half-carved into the rock, and is surrounded by mountains riddled with passages and gorges. It is one of the world’s most famous archaeological sites, where ancient Eastern traditions blend with Hellenistic architecture.
Petra was recently named one of the New Seven Wonders of the World. I can’t help but think that part of the reason it was picked was because it was a filming location for one of the Indiana Jones movies. I say that because there is usually only one photo of Petra which people every see, and that is the Treasury Building. While the Treasury Building is the most well preserved of the carved structures in Petra, there is a lot more to the location. You can spend a full day exploring Petra and be very tired at the end. Not only is it big, there is a lot of vertical distance to climb.