Revillagigedo (Socorro)

Everything here runs on the boat's clock. Trips sail from the Baja cape, cross open ocean for the better part of a day and a night, then settle into several dives a day around the same handful of sites for the rest of the week. There is no shore option, no day-boat alternative and no changing your mind mid-trip: you dive what the swell allows, inside a national park that requires permits and a check-in with the naval detachment on Socorro. Briefings happen on deck between meals, and the last day is the crossing home.

The islands are bare volcanic rock with essentially no coral reef. Dives work lava ridges, boulder slopes and pinnacles that fall away into open ocean, so most of the interest sits off the structure rather than on it. Sites differ mainly in how much water is moving. Some are gentle enough to drift a ledge and watch; the exposed rocks put divers in surge at the top and current on the corners, with up- and downdrafts around the edges that need constant attention.

Entries are usually negative, off a skiff, straight down into blue water, with live-boat pickups afterwards, so an SMB and the discipline to stay as a group are standard. The mantas are the giant oceanic species, the largest of them several metres across, and the encounters run on the animals' terms: they hold station above a group and come back for exhaled bubbles. Touching them is prohibited and guides enforce it. Shark diving is a matter of holding position on a corner and watching passing traffic rather than pursuing it.

This is a trip for divers who already have open-water, current-exposed dives logged; boats commonly ask for a minimum logged count, and nitrox is close to standard. It is not the place to build early experience, and it offers little for macro photographers. June to October is written off for heavy seas, so itineraries run from about mid-November to May and book far ahead, with the humpback window falling in the middle of that stretch rather than at either end. Park fees are usually charged on top of the fare.