Jellyfish Lake has got to be the most unusual place I've ever snorkeled. It's a freshwater lake, about a ten-minute hike from the coast, filled with a species of jellyfish that either don't sting or sting mildly. They follow the sun and get their energy from photosynthesis (thanks to some algae they live with). You can't avoid bumping into them -- and they into you -- if you swim in the part of the lake where they're thickest at that time of the day.
(These photographs are Copyright © 2002 and 2005 by Jerry Peek. Much higher-resolution versions of most images, and many other images too, are available at Jerry Peek Photography. Photos are available at reduced prices, or free, for non-commercial use.)