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May 21-June 6th, 2011. Peru, on a 100 year anniversary of Machu Picchu's first publication in the National Geographic, a 10 day expedition sets out to trace the explorer Hiram Bingham's path to Inca's most sacred city. Here, as the night temperatures drop below 20 degrees Farenheit, the morning icicles form in the stream in the sanctuary valley just before the Choquetecarpo pass on the trail from Choquequirao to Vitcos. Piotr Redlinski for The New York Times.