After you've seen this cave swim, you'll be making reservations for the Mediterranean.
It's really not certain where this is, but enough people say that it's Greece, so I'm going with it.
Once you've seen what it looks like to swim through, you'll be looking for your long-packed-away bathing suit.
If you can't find it, you'd go anyway.
Start making your fantasy list of people you want to do this with right now. What's better: the crystal blue water, or the stunning light seeping into that cave?!
This is the stuff that waterproof cameras are made for!
Make those reservations yet?