9.5567°S, 78.2358°W.
Chanquillo is a fourth-century BCE astronomical and ceremonial complex on the desert coast of the Casma Valley in Ancash, Peru — and the oldest known solar observatory in the Americas. The site is built of stone, adobe, and earth and centres on the Thirteen Towers, a 300-metre line of cuboid stone towers running along a low ridge. From two designated observation points to the east and west of the line, the rising and setting sun aligns with successive towers throughout the year, providing a calendar accurate to within a single day. The towers were built around 250 BCE and remained in use for several centuries. The site also includes a fortified temple complex with concentric defensive walls. Chanquillo's astronomical function was confirmed in a 2007 Nature publication by Iván Ghezzi and Clive Ruggles. UNESCO inscribed the site as a World Heritage Site in 2021.
Chanquillo is the oldest solar observatory in the Americas, and it still tracks the sun the same way it did when it was built.