The history of Cancún , Cozumel , and really, the entire Yucatán Peninsula  is deeply intertwined with its unique geology and ecology. From the ancient Maya to modern-day tourism, the land and its resources have shaped the course of Yucatecan events.
And the Yucatán, in turn, has helped shape the course of Mexican history, from being the stage upon which the early Spanish conquest was conducted to helping rescue a moribund Mexican economy in the 1980s. An understanding of the Yucatán Peninsula’s land, ecology, culture, and politics is vital to understanding the region today.
It has more than 1,600 kilometers (994 miles) of shoreline, with the Caribbean Sea to the east and the Gulf of Mexico to the north and west. To the southwest are the Mexican states of Tabasco  and Chiapas , and directly south are the countries of Belize  and Guatemala .
Geologically, the Yucatán Peninsula is a flat shelf of limestone, a porous rock that acts like a huge sponge. Rainfall is absorbed into the ground and delivered to natural stone-lined sinks and underground rivers. The result is that the Yucatán has virtually no surface water, neither rivers nor lakes. It also has very few hills. The geology changes as you move south, and the first sizable river—the Río Hondo—forms a natural boundary between Belize and Mexico.
The northern and western coasts are bordered by the emerald waters of the Gulf of Mexico. Just inland, the land is dotted with lagoons, sandbars, and swamps. The east coast is edged by the turquoise Caribbean, and the glorious islands of Isla Cozumel , Isla Mujeres , and Isla Contoy  lie just offshore. Along the coast runs the Mesoamerican Reef, the second-longest coral reef in the world.
Over the course of millennia, water that seeped below the Yucatán’s porous limestone shelf eroded a vast network of underground rivers and caves. When a cave’s ceiling wears thin, it may eventually cave in, exposing the water below. The Maya called such sinkholes dzo’not, which Spanish explorers recorded as cenotes.
Most cenotes are extremely deep and interconnected by way of underground channels. A cenote’s surface may be near ground level, but more often it is much farther down, as much as 90 meters (295 feet) below ground level. In those cases, the Maya gathered water by carving stairs into the slick limestone walls or by hanging long ladders into abysmal hollows that lead to underground lakes.