Okay, so swimming in caves doesn't sound quite as glamorous as swimming in waterfalls, but experientially it was awesome, and on the beauty stakes it was pretty damn gorgeous too.
The first picture is of a cave under a monastery (insert evil laugh) - I wonder where it goes (down, down, down, down into the blackness). It is called the Piula Cave Pool and the cave went farther back (and round a corner) than I dared to go, even feeling quite comfortable with a closeness to Satan.
Now with the next photo, you have to get past the name - The Sua Ocean Trench - and just ogle the beauty, whilst trying to ignore the long, long ladder of doom you need to climb down (and up) to get into and out of the water (which was tidal, and came complete with fishes).
When you swim into the dark hole at one end, you come out at another green hole, deep in the ground, with no easy way out, except of course, swimming back to the ladder of doom!