El Túnel

The reef here is cut through. Coral has grown over and across channels in the structure to leave short tunnels and archways, and working through them one after another is the dive rather than an incidental feature of it. Depth sits in the mid teens throughout, so there is time to go back and take a second pass at any passage worth it.

Between the openings it is a standard stretch of the Punta Cancun line: sea fans standing into the current, barracuda holding above, spotted morays in the gaps. The formations are described as dramatic and they are the reason to pick this stretch over its neighbours, which run flatter.

Every reef on this line has some relief. El Túnel is the one where the relief closes over your head. The passages are formed by coral growth rather than by rock, which makes them a different shape from the eroded swim-throughs you meet on limestone coasts: rounder, more irregular, and alive on every surface.

The tunnels are the attraction and the hazard in the same breath. They are short, lit and open at both ends, but they put coral within arm's reach on all sides, and a good proportion of it stings. Buoyancy first, sightseeing second.

It is around forty minutes out from the Cancun dock and usually the second dive of the morning after a wreck, so plan your gas accordingly rather than treating it as a fresh tank on a shallow reef.