Fodor's Expert Review Aktun-Chen

The name is Mayan for "the cave with cenotes inside," and these amazing underground caverns—estimated to be about 5 million years old—are the area's largest. You walk through the underground passages, past stalactites and stalagmites, until you reach the cenote with its various shades of deep green. There's also an on-site canopy tour and one cenote where you can take a swim.  This top family attraction isn't as crowded or touristy as Xplor, Xel-Há, and Xcaret.