Ogasawara Islands

The ship's rotation, not your calendar, sets the shape of the trip. It sails from Tokyo on a fixed cycle of roughly a week, so stays come in set blocks, and you take whatever weather falls inside yours. Operators are small owner-run outfits, boats carry a handful of divers, and a day out is usually a mixed one: a dive, a run offshore to look for dolphins or whales, then a second dive somewhere out of the swell.

These are oceanic volcanic islands that never joined a continent, and it shows underwater in a fish list that includes species most divers will not have logged elsewhere. Steep-sided rock, boulder fields, arches and cave mouths dominate, with coral growing in patches on the rock rather than forming a continuous reef. The exposed outer coasts hold the cleanest water; the lee-side coves are the fallback in a blow, and one of them holds a shallow wreck, hull breaking the surface, generally described as a wartime loss.

Dolphin encounters are done on snorkel rather than scuba. The boat finds a pod, the crew reads whether it is travelling or resting, and swimmers slip in and free-dive alongside if the animals are willing; spinners tend to keep moving, bottlenose are more likely to come and look, and nothing about it is guaranteed. Whales are watched from the boat under local approach guidelines rather than swum with, and landings on Minami-jima run separately, guided and capped under village rules.

Come if the journey is part of the appeal and you are content with an expedition rhythm: few operators, little spare kit, no quick way home, and plans rewritten by the sea state. An evacuation here means a Self-Defense Force seaplane rather than an air ambulance an hour away, so honest current experience matters more than a long logbook. The calm stretch runs from April into October; the winter whale window is real, but the crossing and the conditions are at their worst then, and that trade-off is the main decision every visitor makes.