Saipan & Tinian

Most days start in a van rather than on a boat. Saipan's headline sites are shore entries reached down tracks and staircases, and the real work is topside: carrying tanks down to the water and, harder, carrying them back up again. Centres check the swell first thing and make the call at the top of the steps, shifting to the sheltered lagoon side when the exposed coast is working. Boat days run across to Tinian and out to the lagoon wrecks, and December through May is the stretch when those crossings are dependable.

These are uplifted limestone islands, and the diving follows the rock. Rainwater has cut fissures, tunnels and blue-lit chambers along the coast, and the porous limestone swallows what falls rather than carrying silt out to sea, which is a large part of why the water is what it is. The ocean-facing sides drop away as walls and current-swept points into deep water, while the western side shelters a shallow lagoon of sand, coral heads and wartime metal. Coral cover is patchy next to Palau or Chuuk; the appeal here is clarity, structure and relics.

That wartime layer runs through nearly every kind of site. The 1944 invasions left the lagoon and the shallows scattered with vehicles, landing craft, aircraft parts, small freighters and at least one Japanese flying boat — most of it shallow, much of it broken up, and a fair amount identified more by local habit than by hard evidence. Access arrangements at the Grotto have changed more than once after storms and accidents, so take the current position from a centre rather than an old trip report. Conditions taper from June into the July-to-November typhoon season.

It suits divers who like the water to have a history and who accept that the logistics are part of the day: staircases, van rides, a tide of your own gear, and a fair chance the plan changes at the top of the steps. Newer divers get plenty out of the lagoon and the easier shore entries, and there is enough shallow wreckage to fill days when the coast is shut. Anyone after dense fish life, effortless entries or a liveaboard week has better options elsewhere in Micronesia.