I almost hate to admit it, but I'm a fan of that ol' Survivor TV show here in the states (people really display their illusions about themselves -- it's interesting) and some of the places they've filmed appeal to me.
One place had a lake that had once been connected to ocean but got cut off, was now freshwater, and contained a lot of jellyfish that had evolved over god knows how long to live in freshwater and had lost their toxic stings with the bargain.
There was a scene of some folks swimming in the lake, surrounded by harmless jellyfish. What a trip. I'd have to do some research to find out where that was though.
**WHOOPS** Not that much research. I just tried that new web search thing I've been hearing about
:
http://en.wikipedia.org/wiki/Jellyfish_Lake