A cave whose entire interior glows electric blue because sunlight enters through a large submerged opening below the tiny…A cave whose entire interior glows electric blue because sunlight enters through a large submerged opening below the tiny surface entrance and is filtered by seawater. The water looks lit from within, and anything white in it turns silver. There is nothing subtle about it. Known to the Romans, Emperor Tiberius used it as a private marine nymphaeum and statues of Neptune and Triton were recovered from its floor. Forgotten for centuries as locals believed it haunted by witches, then 'rediscovered' in 1826 by German writer August Kopisch, whose account made it a Grand Tour obsession. Anchorage: Anchor off Capri's north coast or berth at Marina Grande; entry is by licensed rowing boat only, you lie flat to pass the entrance. Hazards: No site-specific hazards noted, brief normally. More