This is truly one of the most memorable sights of my lifetime, seeing the Khazanah through the narrow opening of the Siq in Petra, Jordan. It is both an architectural and natural wonder, although the facade was carved out of the rocks, the colours of the rocks are natural and have been so for centuries. No visitor to this place will leave without taking this classic shot.

(I also have a similar one in this gallery, taken four years ago under quite different lighting conditions)