Kantun-Chi Ecopark

An underground river is what Kantun-Chi has that the roadside cenotes around it don't. On a guided tour of 45 minutes to an hour you swim and wade through it in a helmet and water shoes, under ceilings shaped by thousands of years of dripping water. Afterwards the ticket gives free time in four open cenotes, with kayaks, hammocks and loungers.

There are several ways to do it. One adds a guided walk through the forest to five cenotes, a snorkel in a private one and a three-course lunch, for about two and a half hours plus the meal. Another skips the river and keeps the five cenotes and the lunch. Every tour needs booking ahead, and you should arrive half an hour early or you are moved to the next slot.

The rules are tight. Life jackets are mandatory, you shower before going in, and no sunscreen, repellent, perfume or lotion is allowed, with bags checked at the gate. Children must be six and at least a metre tall. Towels are not included. The river is not recommended for anyone claustrophobic, pregnant, or with heart, breathing or mobility problems.