El Caracol

Called El Caracol by the Spaniards for its interior spiral staircase, this observatory, to the south of the Ossuary, is one of the most fascinating and important of all Chichén Itzá's buildings (but, alas, you can't enter it). Its circular design resembles some central highlands structures, although, surprisingly, not those of Toltec Tula. In a fusion of architectural styles and religious imagery, there are Maya Chac rain-god masks over four external doors facing the cardinal points.

The windows in the observatory's dome are aligned with the appearance of certain stars at specific dates. From the dome the priests decreed the times for rituals, celebrations, corn-planting and harvests.