Night dives off the remote Cocos Island (Costa Rica) are very exciting because you are almost certain to encounter dozens of white-tip sharks hunting among the rocks. They have plenty of natural food available to them here, and they are not actually very aggressive toward humans anyway, but I had to make the title sound more interesting! Nonetheless, it is still an exciting experience to constantly see sharks swimming in and out of your little beam of light in an otherwise very dark ocean, especially as they swim right at you or between your fins!