This is the corners of The Church and the Convent of the Nunnery at Chichen Itza, and is one of the best architectural examples of the Puuc style found at this site.
The Chichén Itzá Observatory or "El Caracol" (The Snail) was dedicated to the study of astronomy and it consists of a tower erected on two rectangular platforms. The Observatory’s name is derived from the unusual stairway inside resembling a snail shell.
The structure, because of its unusual placement on the platform and round shape (the others are rectangular, in keeping with Maya practice), is theorized to be a proto-observatory with doors and windows aligned to astronomical events, specifically around the path of Venus as it traverses the heavens.
Of 29 possible astronomical events (eclipses, equinoxes, solstices, etc) believed to be of interest to the Mesoamerican residents of Chichén Itzá, sight lines for 20 could be found in the structure. Since a portion of the tower resting on El Caracol has been lost, it is possible that the other measurements will never be ascertained to have been observed.
See where this was taken on Google Maps.