At the far northwest corner of Kalasasaya is Tiwanaku’s best-known structure, the 10-ton Puerta del Sol. This megalithic gateway was carved from a single block of andesite, and archaeologists assume that it was associated with the sun deity. The surface of this fine-grained, gray volcanic rock is ornamented with low-relief designs on one side and a row of four deep niches on the other.
The gateway was most likely originally located in the center of Kalasasaya Platform and was used as a calendar, with the sun striking specific figures on the solstice and equinox.
There’s a smaller, similar gateway carved with zoomorphic designs near the western end of the site that is informally known as the Puerta de la Luna.