Machu Picchu is an ancient Inca citadel located at the summit of a mountain in the Urubamba Valley, in southeastern Peru. Built in the 15th century during the reign of Emperor Pachacútec, it is one of the most famous and mysterious archaeological sites in South America. The citadel was abandoned before the arrival of the Spanish and remained hidden for centuries, until it was rediscovered in 1911. In 1985, it was declared a World Heritage Site by UNESCO and is considered one of the New Seven Wonders of the World.