Sanganeb North Point

Sanganeb is a true atoll a few hours off Port Sudan, crowned by a working lighthouse whose keepers wave at the boats, and its North Point is the reason the atoll appears on every Sudanese itinerary. Terraces step down from the rim into blue water, and in the cooler months scalloped hammerheads school along their outer edge at dawn - sometimes a handful, sometimes a wall of animals that swallows the view. Grey reef sharks work the plateau at all hours, dogtooth tuna cruise the drop, and the reef structure itself, protected within a national park and now a World Heritage listing, is in conspicuously fine condition. The climb up the lighthouse between dives, with the whole atoll turquoise below, is the surface interval nobody forgets.

The moment you come for: Dawn hammerhead schools; the lighthouse climb; atoll walls in heritage-grade condition.

Topography: Terraced plateaus stepping off an atoll rim into deep open water

Entry: The atoll's exposed northern tip; dives drop onto the plateau edge at first light when the sharks ride the thermocline.

Hazards: Strong current at the point; early-morning blue-water work; the nearest chamber is effectively a country away.

Conservation: Part of a marine national park inscribed on the World Heritage list in 2016; its condition reflects decades of minimal pressure.

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