The Revillagigedo archipelago sits some four hundred kilometres off the Colima coast: four volcanic islands — Socorro, San Benedicto, Clarión and Roca Partida — with no inhabitants beyond a small naval garrison, and a marine park of 148,000 km² around them, the largest in North America. UNESCO listed it in 2016.
Divers call it Socorro, and it is on most serious lists of the best big-animal diving in the world. The draw is the giant oceanic manta, with wingspans past seven metres, which approach divers and appear to seek out the bubbles. Alongside them: schooling hammerheads, silvertips, Galápagos and silky sharks, bottlenose dolphins that initiate contact, and humpback whales between January and March, often audible underwater before they are visible.
You can only come by liveaboard. Boats leave from Cabo San Lucas — a crossing of 24 to 30 hours — and trips run eight to eleven days, from November to May. There is no day diving, no shore access and no tourism of any other kind; landings on the islands are generally prohibited.
Conditions are open ocean: currents, surge, and water from 21 to 27°C. Operators normally require an advanced certification and a reasonable number of logged dives, and they are right to.