Semicircular construction on a solid rock. In this building are two trapezoidal windows and according to the chroniclers, in the time that was inhabited, had incrustations of precious stones and gold.
It is formed by a series of constructions that dominate the whole of the Citadel. It has a semicircular shape and is on a solid rock with a natural curvature of 10.5 m. Finely worked stone blocks have been used. To the north side stands a door with gilded jambs. To the west of this temple there is a rectangular courtyard with nine niches interspersed with stone nails.
The “Temple of the Sun” was originally a very sheltered complex. In Inca times only the priests and the Inca could use these temples, because they remained closed and protected. People performed their popular ceremonies in open areas or squares such as in Machu Picchu or Cusco.
The entrance to the Temple of the Sun had a double, magnificent wooden door, which on its interior surface had a security system with stone rings. On the lintel of the door must have hung and tied two stakes, inside the small boxes carved in the interior jambs.
The temple itself was built on a huge boulder. The temple has semicircular shape. Its back wall is straight and the temple was built with Inca architecture, that is, with superposed stones with exceptional ability to achieve near perfect joints. The semicircular wall has two windows, one facing east and the other facing north. According to modern scientists these two windows constituted the most important solar observatory of Machu Picchu. Through the window facing the east was possible to accurately measure the winter solstice, depending on the projection of the shadow of the central stone.
Both windows have the false ribbon carved out of the face which certainly served to support the elements that made solar observations and measurements easy. In the center of the temple there is an altar of carved stone that served to carry out the various ceremonies that honor the Sun. This is where the animal sacrifices were executed, to analyze their hearts, lungs and viscera, so that the priests could predict the future. Also here the Inca had to drink the chicha along with his father the Sun. The back wall has a window with small carved holes known as the Window of the Serpent (name given by Bingham).
The holes are very similar to those found in the Temple of the Stars, in the Qorikancha of Cusco, which according to Garcilaso kept ornaments of stone and precious metals. Possibly, these holes had similar function. The straight temple walls have trapezoidal niches on their inner faces that served to store different idols and offerings. Some authors indicate that originally this temple had a conical thatched roof, and they denominate it like Suntur Wasi or Military Tower.