Petra is impressive – established sometime in the 6th century BC as the capital city of the Nabataeans – they carved the entire city out of the rock. They didn’t build columns – they kept carving the rock until they had columns. Given the back-story, it’s some of the most impressive architecture I’ve seen. I highly recommend.
The Monastery (above) and The Treasury (3rd & 4th photos) were my favorite two.
The Monastery, Petra’s largest monument, dates from the 1st century BC. It was dedicated to Obodas I and is believed to be the symposium of Obodas the god. This information is inscribed on the ruins of the Monastery. [wikipedia]