In the midst of a tropical mountain forest covering the eastern slopes of the Peruvian Andes, lays one of the world’s most important archaeological sites: mystical Machu Picchu – “The Lost City of Incas”.
This 15th-century Inca citadel whose name means “old peak” in Quechua, is found just a little northwest of Cusco, Peru’s most visited city. The city is situated on a mountain ridge 2,430 metres (7,970 ft) above sea level.It is located in the Cusco Region, Urubamba Province, Machupicchu District in Peru,above the Sacred Valley, which is 80 kilometres (50 mi) northwest of Cusco and through which the Urubamba River flows.

Source: Sam Travel Peru
The mountain peak Machu Picchu sits upon, seems to disappear into the clouds, leaving the city completely invisible from the Urubamba River (referred to by the Inca as the “Sacred River”) that flows 610 meter below. With the sacred peak of Wayna Picchu at its back, the city sits between two mountain peaks – Machu Picchu and Huayna Picchu.
Source: Lonely Planet
Most archaeologists believe that Machu Picchu, the icon of Inca civilizations was built as an estate for the Inca emperor Pachacuti (1438–1472).The Incas built the estate around 1450 but abandoned it a century later at the time of the Spanish Conquest. Although known locally, it was not known to the Spanish during the colonial period and remained unknown to the outside world until American historian Hiram Bingham brought it to international attention in 1911.

Source: Strange Wonderful
Machu Picchu was built in the classical Inca style, with polished dry-stone walls. Its three primary structures are: “The Inti Watana“, “The Temple of the Sun“, and the “Room of the Three Windows“. Most of the outlying buildings have been reconstructed in order to give tourists a better idea of how they originally appeared.By 1976, thirty percent of Machu Picchu had been restored and restoration continues.

Source: Peru Inca Trail

Source: Chrystal – Clear
Machu Picchu was declared a Peruvian Historical Sanctuary in 1981 and a UNESCO World Heritage Site in 1983.In 2007, Machu Picchu was voted one of the New Seven Wonders of the World in a worldwide Internet poll.

Source: Chrystal – Clear
In a spectacular location, it’s the best-known archaeological site on the continent. This awe-inspiring ancient city was never revealed to the conquering Spaniards and was virtually forgotten until the early part of the 20th century. In the high season, from late May until early September, 2500 people arrive daily. Despite this great tourist influx, the site manages to retain an air of grandeur and mystery, and is a must for all visitors to Peru. June through August are the busiest months.

Source: Get Your Guide
Additional Info: Wikipedia, Lonely Planet, Chrystal Clear