Réunion

The day is organised from the marina at Saint-Gilles and the ramp at Saint-Leu, mostly as morning two-tank trips on small boats. The shelf is narrow, so the run out takes minutes and boats are back before lunch. The rhythm comes from the French club system: you book onto a departure and dive in a guided group to the guide's plan, which is a change of pace for anyone used to buying tanks and going their own way. Briefings default to French, though the larger centres are used to visitors.

The seabed is young volcanic rock with coral growing over it, and it reads nothing like an atoll: basalt ridges, sand chutes and boulder ground with hard coral colonising the high points. The west coast stacks its diving by depth, from sheltered lagoon shallows, through wreck ground in the middle, out to drop-offs and offshore rises where the slope tips into blue. The deeper of the two wrecks lies at 55 m, outside recreational limits and a technical trip rather than a stop on a morning double. Visibility runs 10 to 30 m and swings with runoff and swell, so the same site can be a different dive week to week.

May to October is the dry, settled half of the year and the dependable window, with humpbacks along the west coast from July into October, often heard underwater before anything is seen. The cyclone end of the calendar runs January to March, and December through February is the softest stretch on the water, though it still dives on good days. Realistically this suits divers who came for the island first - the volcano, the cirques, the trails - and want good, undemanding dives fitted around it, rather than travellers whose whole trip is built underwater.