On the way back from looking for whales, Noah took us to Mariners Cave, a spectacular sea cave that you can only enter by swimming through an underwater tunnel. It is a real leap of faith, and I think that the first people must have been completely nuts. You swim up to a big black hole in an underwater cliff and even though you are pretty sure that in a short distance it will be fine, every survival instinct developed over the last million years is screaming not to go in there. The entrance is completely black and you have to just commit and swim in. Last thought, "I hope that this is the right cave."

Swimming in, the dark envelopes you and then - finally- you see the underside of the surface ahead and your fingers break through and then you come up inside the cavern. Floating in the cave you can see the sides and the ceiling far above covered in stalactites eerily lit from beneath by what turquoise light made it this far through the crystal water of the tunnel. The light refracts through the entrance and shines up from below onto the roof and the constant movement of the water continually adjusts the focus. The backlit entrance was a wonderfully reassuring anchor to the outside world as you scan the bottom 50 feet below for the pirates treasure that must be here somewhere.

Then the water surges gently into the cave and the pressure in the cave changes. First your ears pop and you wonder how much more the water level is going to rise, and suddenly the entire cavern is filled with dense fog. There is a moment of confusion as you look for familiar landmarks then the air instantly clears as the water surges out and is suddenly bright again.

Timothy, Mary and I all swam in after a bit of persuasion, and once was more than enough for Mary. Even though the cavern was the size of a church, there was a strange claustrophobic feeling as the pressure rose in the room and the air filled with fog. Timothy and Mary were very happy to be back on the little boat.