Machu Picchu (from Quechua, Machu Pichu, meaning 'mountain or old peak', pronounced [ˈmɐt͡ʃʊ ˈpɪkt͡ʃʊ]) is the present name of an ancient Inca settlement (llacta) built before the 15th century, located in the Eastern Cordillera of southern Peru, in the Andes, at 2,430 meters above sea level. It is located in the department of Cusco (province of Urubamba, district of Machupichu), on the Sacred Valley of the Incas, 80 kilometers northwest of Cusco, where the Urubamba River flows through the mountain range and forms a canyon with a tropical mountain climate. Machu Picchu is part of an archeological and ecological conservation area that bears the same name. According to some studies, its original name may have been Llaqtapata or Patallaqta.

Documents from the mid-16th century indicate that it was a private place. However, some of its most outstanding constructions and the evident ceremonial character of the main access road suggest that its origin is prior to Pachacútec and that it could have been used as a religious sanctuary. Both uses, residence and sanctuary, would not be incompatible. Although its possible military function is debated, the popular terms "fortress" or "citadel" may not be entirely accurate.

Machu Picchu is considered a masterpiece of architecture and engineering. Its unique architectural and landscape features, along with the mystery surrounding the site, have made it one of the world's best-known tourist destinations and one of the seven wonders of the modern world.

Built in the classic Inca style, Machu Picchu features polished dry stone walls. Its three main structures are the Intihuatana, the Temple of the Sun and the Temple of the Three Windows. Many of the outlying buildings have been restored so that visitors can get a better idea of their original appearance. By 1976, 30% of Machu Picchu had been restored, and this work continues.

Machu Picchu and its surrounding area were declared a Peruvian Historic Sanctuary in 1981 and have been on UNESCO's World Heritage List since 1983, as part of the cultural and ecological complex known as the Machu Picchu Historic Sanctuary. On July 7, 2007, Machu Picchu was named one of the new seven wonders of the modern world at a ceremony in Lisbon, Portugal, attended by 100 million voters worldwide. The Machu Picchu and Huayna Picchu mountains are part of a large geological formation known as the Vilcabamba batholith, in the Cordillera Central of the Peruvian Andes. They are located on the left bank of the Urubamba Canyon, formerly known as Quebrada de Picchu. At the foot of the hills flows the Vilcanota-Urubamba River. The archaeological site is located halfway between the peaks of both mountains, 450 meters above valley level and 2438 meters above sea level. The built area is approximately 530 meters long and 200 meters wide, with 172 buildings in its urban area. It is located in the Peruvian yungas ecoregion.

The ruins are located within an intangible territory of the National System of Natural Areas Protected by the State (SINANPE), called the Machu Picchu Historic Sanctuary, which covers 32,592 hectares (80,535 acres or 325.92 km²) of the Vilcanota-Urubamba River basin, known as the Willka mayu or 'sacred river' of the Incas. This sanctuary protects several endangered biological species and several Inca sites, Machu Picchu being the most important. The archaeological area is accessible via post-Inca trails or by the Hiram Bingham Highway, which ascends from the old train station at Puente Ruinas, at the bottom of the canyon. However, both options require the payment of an entrance fee to the complex. This road is not part of Peru's national road network; it starts in the town of Aguas Calientes, which is only accessible by rail (three hours from Cusco) or helicopter (30 minutes from Cusco). The lack of a direct road to the sanctuary is intentional, to control the flow of visitors, given that the area is sensitive to crowds. Despite this, Aguas Calientes has grown unregulated, with a tourist infrastructure that includes hotels and restaurants of various categories.

The archaeological site is built on the Vilcabamba batholith, formed by intrusive rocks approximately 250 million years old, mainly white to grayish granite, interspersed with tonalites and talcose schists. This granitic massif presents numerous faults and diaclases that influence its current relief and evolution. The Geological Map of the Machu Picchu Quadrangle (27-q) of the Peruvian Geological Mining and Metallurgical Institute identifies two large regional faults, called the Huayna Picchu and Machu Picchu faults, oriented northeast to southwest, which have not had any recent activity. The Picchu gorge, located between the Andes and the Amazon jungle, was colonized by Andean populations from Vilcabamba and the Sacred Valley in Cusco, seeking to expand their agricultural frontiers. Archaeological evidence shows that agriculture was practiced in the region since at least 760 BC. During the Middle Horizon period, from 900 A.D. onwards, there was a demographic increase by undocumented groups that could have been linked to the Tampu ethnic group of the Urubamba. These people could have been part of the Ayarmaca federation, competitors of the first Incas of Cusco. During this period, the "built" agricultural area (andenes) was significantly expanded, although there is no evidence of buildings at the specific site of Machu Picchu before the 15th century. The built area at Machu Picchu is 530 meters long by 200 meters wide and includes at least 172 enclosures. The complex is divided into well-defined areas: the agricultural zone, with cultivation terraces to the south, and the urban zone, where its inhabitants resided and where the main civil and religious activities took place. These areas are separated by a wall, a moat and a stairway that follow the eastern slope of the mountain. Building a stone city on an "isthmus" between two mountains and two geological faults in a region prone to earthquakes and heavy rains represents a great challenge for any builder: to avoid the collapse of the complex. According to Alfredo Valencia and Keneth Wright, "the secret of Machu Picchu's longevity is its drainage system". Indeed, the floor of the non-roofed areas has a drainage system consisting of layers of gravel and rocks, designed to prevent the accumulation of rainwater. There are 129 drainage channels extending throughout the urban area, designed to prevent splashing and erosion, flowing into the ditch separating the urban and agricultural areas, which served as the main drainage for the city. It is estimated that sixty percent of Machu Picchu's construction effort was devoted to foundations on terraces filled with rubble for proper water drainage.