Lost Blue Hole

East of Nassau, a near-perfect circle about thirty meters across opens in the sand at twelve meters and drops far beyond recreational range. The rim is the dive: coral heads ring the edge like a crown, nurse sharks stack up in the hollows, sometimes half a dozen deep, and schools of jacks and snappers rotate above the void. Divers typically circle the lip, drop a short way into the shaft to feel its scale, then return to the rim's fish traffic. Summer aggregations inside the hole can be dense enough to dim the light below.

The moment you come for: Sheer-sided ocean blue hole, piles of nurse sharks on the rim

Topography: Sand plain broken by a coral-rimmed circular shaft

Hazards: The shaft invites uncontrolled depth; set limits before descending and watch gauges against the featureless walls.

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