Machu Picchu is an ancient Inca citadel set high in the Andes Mountains in Peru, above the Amazon rainforest. It was built in the 15th century but abandoned a century later at the time of the Spanish conquest of the Inca Empire. It lay hidden and largely undisturbed until 1911 when it was rediscovered by Hiram Bingham. Now a UNESCO World Heritage site, it is Peru's most visited tourist attraction but tourism poses threats from overcrowding and erosion that require active management and limits on visitor numbers to preserve the site.