Carved into red sandstone cliffs in southwestern Jordan, the lost city of Petra was the capital of an ancient kingdom. Once a thriving center of trade, having lain in ruins for centuries, Petra is now one of the world’s New Seven Wonders. Each year, the 102-square-mile site typically attracts over a million visitors to what was once the ancient Kingdom of Nabatean. Yet most tourists only catch a glimpse of its majesty. “We have uncovered just 15 percent of the city,” archaeologist Zeidoun Al-Muheisen of Jordan’s Yarmouk University told National Geographic. “The vast majority—85 percent—is still underground and untouched.” Visitors to Petra first follow an almost mile-long winding gorge, known as the Siq, decorated with sculptures of gods and animals along the path, into the center of the recovered architecture. Petra’s “treasury,” called Al Khazneh, is the first sight along the journey. Rising 127 feet high and 82 feet wide, its formidable sandstone columns …