The rose-red city of Petra, one of the wonders of the ancient world, has parts that are miraculously preserved and others that have been eroded and sculpted by floods and the elements. Until Swiss explorer Johann Ludwig Burckhardt "rediscovered" it in 1812, Petra had been forgotten for centuries. It can be reached on foot by the Siq Gorge, a narrow, winding passageway at times no wider than 6 feet, with rock faces on either side as high as a four-story building. At the end of this eerie, mile-long passageway, a magical sight looms through the fissure ahead: the Khaznah or Treasury, a soaring, classical Greek-style temple hewn right into the sheer face of a 130-foot cliff. It dates back to 56 B.C. and is one of the best-preserved of Petra's wonders. Petra, which means "rock," was a fortress city and thriving trade center whose inhabitants carved houses, temples, and tombs, sometimes with extremely elaborate and columned facades, out of the natural canyon walls. The area, 2 square miles in size, is as remarkable for the number and variety of the rock-cut monuments as it is for the myriad hues of the rock and the ever-changing play of light as the desert sun makes its way across the sky.