New Caledonia

Most diving is done as half-day, two-tank runs from Nouméa, and the width of the lagoon sets the rhythm: the barrier reef is far enough out that boats leave early, dive and are back for lunch. Pass dives are scheduled against the tide rather than the clock, so a briefing time can shift by hours from one day to the next. Trips rarely cancel outright, because when the outer reef is rough the crews fall back to the islets and coral inside the lagoon and dive something calm instead.

Three quite different kinds of diving sit inside one territory. Inside the lagoon there are shallow coral flats and sand around the islets off town, easy and current-free, which is where courses and check dives happen. Out on the barrier the passes are the problem to solve: water funnels through on the tide, and the job is dropping accurately onto a corner and holding there while the resident fish work the flow. The Loyalty Islands are different geology again — uplifted coral ringed by drop-offs into open ocean.

The Aiguille de Prony is the oddity worth planning a day around. Hyperalkaline groundwater, filtered through the ultramafic rock of the far south, vents on the floor of Prony Bay and precipitates carbonate where it meets seawater, so the structure grows upward around the seeps. It is living geology rather than reef, the growth on it looks nothing like a coral site, and the bay water is darker and greener than anything on the outer reef. Elsewhere the dives people remember are the pass corners, where the tide does the work and you hold position and watch.

This suits divers who want variety inside one trip and do not mind arranging it, since an easy islet dive, a pass on a running tide and a Loyalty Islands wall are effectively three trips stitched together by short domestic flights. It is French-speaking, briefings default to French and English is worth confirming when you book, and prices track metropolitan France more than the rest of the Pacific, though good roads, hire cars and food make non-diving days easy. Divers after one fixed site for a week, or guaranteed big-animal encounters, will do better elsewhere.