A ferry ride from Cozumel brings us here to the gates of Xibalba, the Maya underworld. We're lured by the cenotes of Riviera Maya, a vast subterranean river system hidden underneath the Yucatan jungle.

Chac Mool is near the town of Puerto Aventuras. The cenote's twisting tunnels transport divers to chambers richly decorated with sculptured columns. Our guide leads us through a maze of caverns and passages. One moment, our light beams stave off unnerving pitch-black nothingness. The next, we hover beneath a tree-fringed skylight in startlingly clear freshwater, bathed in sun rays filtering through the foliage.

Too soon it's time to leave this enchanted otherworld and return to reality.

"With the combination of the fossils on the cave floor and the stalactites hanging overhead, you're wondering, 'Where am I?'"

InDepth

Cozumel (CZM) is the closest international airport, with a short connecting ferry ride. But flights are more plentiful--and cheaper--to Cancun (CUN), a little farther away from cenote central. Mexicana, Aeromexico, US Airways, Continental, Jet Blue, Northwest, Delta, United and Spirit all serve Cancun. American, Mexican and Continental serve Cozumel. For more info, go to rivieramaya.com

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