Intihuatana (Machu Picchu).
Carved directly into the bedrock of the mountain summit, the Intihuatana points directly at the sun during the winter solstice. At noon on the equinox days, it casts no shadow at all. On June 21st, it casts the longest shadow on its southern side, and a much shorter shadow on the northern side on December 21st.
The stone column tilts 13° north, rising from a slightly inclined plane. A granite block may have been an altar, carved shelf or bench. The base is rectangular.
The Inca had many such ritual stones, but most were destroyed by the Spanish during the late 1500s, by the order of Viceroy Francisco de Toledo, the fifth Viceroy of Peru. However, as the Machu Picchu ruins were undiscovered by the invaders, this one remained undisturbed.