North Neptune Islands

Everything runs off the boat. Charters leave Port Lincoln, six hours by road from Adelaide, and the operator holds the permit that lets you enter the protected area, so that side of it is part of the charter rather than something you arrange. One cage is moored at the surface and works at about 2 m; it runs on breathing air supplied from the boat rather than tanks, which is why no prior training is needed to get into it.

The other way to do it is the cage lowered to the seabed at 18 m, which one operator runs and which asks for an entry-level certification such as CMAS 1 Star or PADI Open Water. The depth is not the point; being on the bottom puts you level with the sharks rather than looking down at them from the surface. The ground falls away quickly here, reaching 80 m within 1.5 km of the northern group, so deep water is close by.

The rule inside the cage is short and absolute: no part of you goes outside the bars and nobody reaches for a shark. The islands themselves are why the animals are here. New Zealand fur seals and Australian sea lions are common across the group and use it for breeding, with a small Australian sea lion breeding population on the North Neptunes. The large island rises to 49 m, with a 29 m islet 300 m off its north-east point, and restricted-area zoning governs access to both the islands and the water around them.