Casa Cenote is unusual: instead of a sinkhole in the jungle, this cenote forms a long, narrow mangrove channel that runs almost to the sea, with brackish water that mixes fresh and salt. The channel is wide enough to paddle a kayak through, and the surrounding mangroves shelter heron, snook, and barracuda — Casa Cenote sits at the mouth of one of the longest underwater cave systems in the world.
There is a resident crocodile named Panchito that occasionally cruises the surface; the staff know his habits and will warn you if he is around. Snorkellers see schools of small fish and the rippling halocline where the waters mix. The site is on the road to Akumal, eight kilometres north of Tulum. Combine it with a meal at the small palapa restaurant next to the parking area.