This is the oldest part of Chichén Itzá, characterised by its typically Mayan Puuc style and its superb decorations on the Iglesia temple. The more recent Caracol, a round astronomical observatory, derives its name ("the Snail") from the central spiral staircase. It was probably designed for observing Venus (note the openings studding the upper chamber), a planet associated with the worship of Kukulcán, or Quetzalcóatl.