One of the more notable structures at Chichen Itza is a complex of Terminal Classic buildings constructed in the Puuc architectural style. The Spanish nicknamed this complex Las Monjas("The Nuns" or "The Nunnery") but was actually a governmental palace. Just to the east is a small temple (nicknamed La Iglesia, "The Church") decorated with elaborate masks of the rain god Chaac.

from wikipedia: http://en.wikipedia.org/wiki/Chichen_Itza