Niihau

The Forbidden Island sits 17 miles southwest of Kauai and is privately owned by the Robinson family, which strictly controls access — but the surrounding reef is accessible by permitted dive charter and represents some of the least disturbed reef habitat in the main Hawaiian Islands. Scalloped hammerhead sharks school in the blue water off the island's western wall, joined by Galapagos sharks and the critically endangered Hawaiian monk seal. Zero fishing pressure and minimal dive traffic have allowed fish populations to reach densities rarely seen in the main islands.