One of the most fascinating of all Mayan ruins, Tulum is located about 80 miles southeast of Cancun and 25 miles southwest of Cozumel. Tulum is the only walled city the Mayans built. It stands by the edge of the Caribbean. When the Spaniards first came upon the site in 1518, they recorded that it was as large as Seville. The Castle stands out among the delicate small-scale buildings. It is a handsome pyramid perched on the edge of a cliff high above the pearl-white beaches below.