On this racing-torrent river, guests hang ten in their mandatory life vests amid roaring whitewater rapids as they surf beneath the slides inside Krakatau. This is the best attraction of its kind that we’ve experienced outside of the Atlantis resort in the Bahamas, but if you’re looking for a lazy river, this ain’t it! A tip for hopeful surfers: paddle upstream as you exit from under the volcano long enough to catch a curl from the wave generator.