Tulum is a town on the Caribbean coastline of Mexico’s Yucatán Peninsula. It’s known for its beaches and well-preserved ruins of an ancient Mayan port city. The main building is a large stone structure called El Castillo (castle), perched on a rocky cliff above the white sand beach and turquoise sea. Near the ruins is the Parque Nacional Tulum, a coastal area with mangroves and cenotes (natural limestone sinkholes).