Beqa Lagoon is a huge, loosely-enclosed area on the south side of Viti Levu Island. The easiest place to dive it from is Pacific Harbor, which is about three hours drive from Nadi, where the big planes land. The best food and the most isolation can purportedly be had at the Marlin Bay Resort, which is offshore.
The lagoon’s name is pronounced BEN-ga, and it’s one of the world’s great places for macro photography. The part that’s best for diving is full of bommies: cylindrical coral heads — circular and with near-vertical sides, from 40 to 200 feet in diameter, projecting up from a 40 to 60 foot bottom to within a few feet of the surface. The lagoon is subject to tidal currents that whip ’round the bommies, bringing nutrients to the animal life, and occasional excitement to divers. Many bommies have caves and overhangs near the bottom. Even the bleak-looking sandy areas between them are full of things like mantis shrimp and fire gobies.