SS President Coolidge

No other wreck of this stature starts at the end of a beach path. The Coolidge, a 1930s trans-Pacific luxury liner carrying over 5,000 troops when she struck friendly mines in October 1942, was run toward shore and now lies on her side down a slope that lets divers build depth day by day: jeeps and rifles in the forward holds first, then the medical stores, the guns, and eventually the first-class smoking room where the porcelain relief of a lady and unicorn has become a pilgrimage object. Nearly all aboard survived; two men did not, and guides tell their story. A week here feels like reading a very large book properly.

The moment you come for: The Lady at depth; cargo holds full of 1942; a shore-entry giant that rewards repeat dives.

Topography: A 198-meter liner-turned-troopship lying on her port side down a sandy slope, bow around 20 m, stern beyond 60 m

Entry: Walk in over a coral flat minutes from Luganville and follow the guide line down to the bow; all diving is guided by local rule.

Hazards: Depth accumulates fast on a guided tour; silt, cables, and true overhead in the interior; deep sections are decompression dives in fact if not in name: treat them so.

Conservation: Protected under Vanuatu law with two lives lost in the sinking: artifacts stay, and local guiding rules exist to keep both wreck and divers whole.

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