Numidia

The Numidia was weeks old when she ran onto Big Brother's northern point in July 1901, and the island has been absorbing her ever since. Her cargo included railway rolling-stock wheels, and a pair still sits near the reef crest at snorkeling depth - the shallowest relic of a wreck that pours down the slope like spilled cargo itself, deck structures at 30-something meters, the deeper hull fading past 80 into technical territory. A century of current has upholstered every surface in soft coral, so the wreck reads as reef and ship at once, patrolled by grey reef sharks and wrapped in anthias. Recreational divers work the upper third on nitrox and watch their computers; the deep sections belong to staged-decompression teams.

The moment you come for: Locomotive wheels at the crest; soft coral on century-old steel; sharks working the wreck line.

Topography: A steel cargo steamer draped down the reef slope from about 8 meters to far beyond 80

Entry: On Big Brother's north tip; entries time the current and exits ride it onto the island's flank.

Hazards: Current across the point; the wreck's slope invites unplanned depth; surge near the crest.

Conservation: An 1901 heritage wreck fused with living reef - anchor damage and souvenir habits have no place here.

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