Cenote Dos Ojos

Underneath, the two are joined by a passage wide enough to snorkel through, and shallow enough that daylight reaches most of it. That is the whole appeal — you are inside a cave with the light still on, floating over rock formations that were dry land when the sea was 120 metres lower. The system it belongs to, Sac Actun, has more than 376 kilometres of mapped flooded galleries, which makes it the longest known underwater cave system in the world.

The park around it is run by the Maya community that holds the land, and takes conservation seriously in the ways that affect you: shower before you get in, no sunscreen, no touching the formations, life jackets for anyone not certified. Six cenotes share the entrance — Dos Ojos, Jaguar, Nicte-Ha, Misterio Maya, Monos and El Pit — and the ticket is per cenote rather than per park.

Snorkel or dive

Snorkelling here is a guided or self-guided float along a marked line inside the daylight zone, with a life jacket and usually a torch. It needs no certification, and it is what most visitors do.

Diving is a different activity with the same address. Cavern diving stays inside the light zone with a guide and is open to any certified open-water diver — the two-tank trip runs the Bat Cave and the Barbie Line, and is about buoyancy control rather than depth. Cave diving, past the daylight, is a separate certification and is not sold casually to visitors. El Pit, at MX$1,800, is the deep site: a shaft with a halocline where fresh water meets salt, and shafts of light that reach well below thirty metres.

If you have one visit and want the photograph, buy Dos Ojos at MX$400. If you are with small children or would rather swim under open sky than under rock, Nicte-Ha at MX$300 is a shallow lily-covered pool with turtles. Jaguar at MX$350 has jump platforms and a zipline and suits teenagers.

The guided visit at MX$1,200 covers several cenotes with a guide, and is the version that makes sense for a group who will not come back.

Cenote Misterio Maya is the geology one: formations rather than open water, and the least crowded corner of the park. Cenote Monos is a walk through near-darkness under thousands of stalactites, which is either the highlight of the day or the part you skip, depending on how you feel about caves. Cenote Jaguar at MX$350 is the loud one — jump platforms and a zipline — and it is where families with teenagers end up.

The park's own guided visit at MX$1,200 exists precisely because working out which of the six you want is hard from the entrance. If there are two or three of you and one shot at it, that is the ticket that removes the guesswork; on your own, buy Dos Ojos and add Nicte-Ha.

A colectivo running Highway 307 will drop you at the entrance road; the walk in from the highway is longer than it looks, and the park runs its own transport from the gate to the individual cenotes. A bicycle from Tulum is not a sensible plan on this road. Most visitors either drive, take a colectivo, or arrive with a dive shop.

Payment is the easy part here, and the exception on this coast: the park takes Visa, Mastercard, American Express, Carnet and Discover, plus OXXO and bank transfer, as well as cash at the window. Booking online gives you a QR code by email, and a cancellation made more than 48 hours ahead is refunded in full — date changes are free by email or WhatsApp.

• Shower first and skip the sunscreen — the rule is enforced, biodegradable included
• Life jacket is included with entry and compulsory for anyone not certified
• Snorkel and fins are rented at the park or brought with you
• Non-slip shoes — the wooden stairs and platforms are wet all day
• Water and something to eat — there is little inside, and the cenotes are spread out
• No drones, no loudspeakers, and quiet in the caves — bats, blind fish and nesting birds