Swimming into the Emerald Cave

People are nervous about this one and they are right to think about it before they do it. The tunnel is eighty metres long and there is a stretch in the middle where it is properly, completely dark.

What makes it fine is the float line. You hold on, your guide leads with a torch, and the group moves together. You do not swim it alone and you do not need to be a strong swimmer.

What it is like inside

Cold at first, then not. The roof drops low enough in one section that you can touch it. Sound behaves strangely — voices come back at you off the walls and the sea moving through the tunnel is much louder than you expect.

And then it opens

A circle of white sand, cliffs on every side going up two hundred metres, jungle at the back, and a disc of sky overhead. It is entirely enclosed. There is no path, no other entrance, and for about fifteen minutes there is nobody else in it.

If you would rather not

Nobody makes you. Guests who sit this one out stay on the boat and swim off the back in the bay, and we have never had anyone regret the choice either way.