São Tomé & Príncipe

Diving here is a small, arrange-it-in-advance affair. A handful of centres work off the two islands, boats are modest and go out when there are enough people to fill them, and a day usually means two dives on one stretch of coast rather than a planned circuit of named sites. There is no dive-shop strip and no liveaboard fleet. The workable approach is to book ahead, take whatever site the operator picks, and let wind and swell decide the rest.

What you drop onto is volcanic. Both islands are basalt peaks on the Cameroon volcanic line, and the coast carries on underwater as stacks, boulder fields and steep faces; hard coral grows here but never builds the structure, so the relief is rock. Nutrient-rich equatorial water swings visibility about from week to week and leaves the reef greener and more productive-looking than a picture-book tropical site. The fish are eastern Atlantic, with some species found almost nowhere else, so a diver arriving from the Indian Ocean will not recognise much.

The payoff for the effort is fish size and density. Grouper hold on the offshore rock at a size that has become scarce on harder-fished coasts, and jacks and barracuda move through in schools, which makes this wide-angle territory rather than a macro hunt; most dives stay inside 30 m on pinnacle tops and their skirts. A few wrecks lie in the bay off the capital, but they are a side trip rather than the reason to come. It suits self-sufficient divers who treat the exploratory quality as the attraction and can absorb the odd day when no boat goes out at all.