Ancient Al-Khazneh Rock-Cut Treasury, Petra, Jordan

An ancient excavation

Millennia after the Egyptians cut and hauled great blocks of stone into sandy wastes to build the pyramids, the Nabataeans had a labor-saving idea: Just build right where the stone is. Now known as Petra (a name derived from the Greek for stone), this city of rose-red sandstone was hewn from the cliffsides back in the 1st century, and now draws almost a million people a year as Jordan's preeminent tourist attraction. Attention is both a blessing and a curse for this seemingly mystical mausoleum, known as Al-Khazneh (the Treasury). Throngs of visitors keep the local economy bustling, but their combined body moisture accelerates the erosion of Petra's intricate buildings, whose sandstone bones are already weathered by the elements.