The Yucatan Peninsula

The asteroid landed here. About 66 million years ago a rock some ten kilometers wide struck the shallow sea off what is now the northern Yucatan, leaving the buried Chicxulub crater and ending the age of the dinosaurs — and the peninsula still carries the mark. The impact shattered the limestone, and where the shattered rock later dissolved, sinkholes opened in a great arc: the ring of cenotes, thousands of freshwater pools that are the only reliable water in a land with almost no rivers at all. Maya cities were built around them. Divers explore them. Nearly the whole human history of this limestone shelf follows, one way or another, from a hole in the ground.

The peninsula separates the Gulf of Mexico from the Caribbean Sea, some 197,000 square kilometers shared by Mexico, Belize and Guatemala. It is a flat platform of porous limestone barely above sea level, so rain sinks straight through into an underground network of flooded caves — among the longest cave systems on Earth — instead of running off in streams. The Puuc Hills in the northwest reach only about 210 meters, though the Maya Mountains at the southern edge in Belize rise considerably higher. Dry thorn forest in the north gives way to true rainforest in the Peten to the south. Offshore lies the Mesoamerican Barrier Reef, the largest in the Americas, and hurricanes cross regularly.

The Maya built Chichen Itza, Uxmal, Coba and Calakmul on this shelf, engineering reservoirs and drawing water from the cenotes, and their descendants still speak Yucatec Maya by the hundreds of thousands: this is a living civilization, not a vanished one. Henequen, the sisal fiber grown for rope, made Merida's fortunes in the nineteenth century and left behind grand mansions and a bitter labor history. Tourism now dominates. Cancun, invented from nothing in the 1970s, and the Riviera Maya draw millions of visitors a year, straining the aquifer that everyone drinks from, since whatever is spilled on the surface reaches the groundwater fast. The Tren Maya railway has sharpened the argument about what growth costs here.

• Belize
  A jungle-and-reef nation where Maya ruins meet the Caribbean country in region
• Guatemala
  The Maya heartland of highland volcanoes and rainforest country in region
• Mexico
  Where ancient civilizations and a modern powerhouse meet country in region
• Caribbean Sea
  The tropical sea of pirates, coral, and a thousand islands defining feature
• Gulf of Mexico
  North America's great basin of oil, hurricanes, and shrimp defining feature
• Mesoamerican Barrier Reef
  The largest reef in the Americas, arcing along four Caribbean nations defining feature
• North America
  The third-largest continent, from the Arctic to the tropics located in