What is the name of the circular observatory at Chichen Itza?

The circular observatory at Chichen Itza is called El Caracol.

El Caracol is a distinctive round structure in the Central Group of Chichen Itza, in Mexico's Yucatán Peninsula. Its Spanish name means “the snail,” a reference to the spiral staircase inside the tower. The building stands on a large square platform and is architecturally unusual because Maya buildings at the site were more often rectangular.

Archaeologists have long interpreted El Caracol as an astronomical observation building. Its doors, windows, and sight lines appear to have been positioned to frame important points on the horizon, including locations associated with Venus and other celestial events. The flat Yucatán landscape offered few natural elevations, so a raised tower would have provided useful views above the surrounding vegetation.

The structure is generally dated to around AD 900 or the early Postclassic period, although its exact construction history is complex. “Observatory” is a helpful traditional label, but scholars continue to debate how precisely the building was used and which alignments were intentional. The other choices are different monuments: El Castillo is Chichen Itza's famous pyramid, while the Ball Court and Temple of the Warriors serve distinct ceremonial or sporting roles.