Palau

Departure times are set by the tide rather than the clock: crews work backwards from when a given corner will have water moving across it, because the same plateau on slack is a much duller dive. A normal day is two or three tanks with a stop on a beach or sandbar between them, and the run out to the south-western barrier reef takes a real bite out of the morning. Liveaboards earn their keep mainly by cutting that transit and getting down to Peleliu and the southern reefs more often.

The terrain sorts into three kinds of dive. Outer walls fall away from a shallow reef flat straight into blue, so you drift with one shoulder to the coral and nothing under your fins. Channels cut through the barrier and squeeze the tide into fast, directional dives that run into the lagoon or out of it depending on which way the water is going. Then there is the limestone itself, dissolved into shafts, tunnels and cavern mouths, so a fair part of the week is spent reading structure rather than reef.

The signature move is hooking in. You fin down onto the lip of a plateau, set a hook into bare rock rather than coral, pay out line and hang there with your hands free while the current does the work and the animals stack up off the edge. Not every dive is that intense: the blue holes and reef tunnels trade current for overhead structure and shafts of light, the sheltered inner bays hold small, slow subjects, and the marine lake is a hike over a limestone ridge and a snorkel, since scuba is not permitted in it.

It rewards divers already comfortable being pushed around: buoyancy that holds in surge, no hesitation about a negative entry, and a willingness to accept that a site gets dropped when the tide is wrong. Less experienced divers can still fill a week on the inner reefs and gentler channels, and guides tend to stream groups by experience on the days the corners fire. Pack for wide angle. The headline dives are big animals seen at distance in moving water, not close, patient macro.