Irizaki

Irizaki diving is minimalist: drop into open blue off the westernmost point of Japan, level off mid-water, and scan. In the cool months scalloped hammerheads school here, sometimes a handful of scouts, sometimes a slow-turning wall of silhouettes that fills the view from left to right. There is no reef to hold, no fixed route, just the guide's fin tips, the group's discipline, and the cold-edged current deciding how far each dive travels. Blank dives happen and the good ones erase them. It is the western Pacific's answer to the classic hammerhead pilgrimages, made rawer by winter seas and the island's frontier scale.

The moment you come for: Schooling scalloped hammerheads, pure blue-water drift diving, winter-season intensity

Topography: Open blue water off a rocky cape dropping steeply toward deep ocean

Current: The Kuroshio brushes the cape; drifts move fast and regrouping mid-water is part of the skill set.

Entry: Negative-entry drops from boats working off Japan's westernmost cape near Kubura; groups drift as one unit behind the guide.

Hazards: Strong current, no fixed reference, boat pickups in swell, and depth creep while watching animals; surface markers and tight buddy contact are mandatory.

Nitrox: Worth it here — profiles sit in the range where enriched air meaningfully extends no-stop time (with the training to use it).