Cayo is a district in western Belize with many parks and ecological reserves. Once the heart of the Belizean Maya world, it’s rich with pre-Columbian archaeological sites. Cayo is known especially for the ruins of Xunantunich, with its 39m-high El Castillo pyramid, and Caracol, the country’s largest Mayan ruin. Many of its once-sacred Mayan caves are open for exploration, including Actun Tunichil Muknal.