Most magical place you've ever been swimming?

Looking for some trip inspiration and I'd love to hear about beaches and swimming holes that just felt too perfect to be real life -- great vibes, amazing scenery, etc.

(So far, some of mine would be Hanalei Bay, Agia Anna on Naxos, and Echo Lake Ledges in Acadia, and a cenote in Mexico that I forget the name of because it was forever ago.)

Any ideas would be much appreciated!