Osprey Reef

Everything here begins with the crossing. Boats leave Cairns, usually work the Ribbon Reefs on the way out, then run through the night across open water, and you wake up on a mooring with no land anywhere on the horizon, because the atoll carries none. From there the day settles into the liveaboard pattern of four or five dives including one after dark, all off the same vessel, with no shore, no shops and nowhere to sit a day out except on deck.

The reef is a rim enclosing a lagoon, and almost all the diving happens on the outside of it. What that means in practice is that nothing below you reads as a bottom, so depth becomes a matter of personal discipline rather than topography; boats hold profiles to recreational limits, and the structure worth looking at sits well above them anyway. Along the rim the face breaks into buttresses, cuts and terraces, and at the northern tip two walls converge into an amphitheatre of ledges divers settle onto while sharks work back and forth in front of them.

The signature dives put reef on one side of you and open ocean on the other. You leave the wall, hang out in the blue and watch what comes past, which late in the year can mean scalloped hammerheads, sometimes in numbers rather than singly, before the rest of the bottom time goes on the shallow coral. The same wall dived twice in a day rarely produces the same result, because everything depends on what happens to be moving through.

This is a trip for divers who are settled in open water and unbothered by depth, current and the absence of any reference below them. It rewards patience and steady buoyancy far more than close-quarters camera skill; macro subjects exist, but nobody books this boat for them. It is also weather-dependent in a way inshore diving is not, since the crossing needs a settled forecast, and operators stand the route down through the January-and-February cyclone months rather than risk the passage.