Vanessa quickly finds a giant lobster hidden in a rock crevice, and we all take turns looking at it. It’s the biggest lobster I’ve ever seen, bigger than a small dog, and it’s brown and white striped. Given its size, it must be ancient. Lobsters can live over one hundred years, and I wonder if this one is a centenarian. Its antennae seem to be countless, and they poke out from everywhere. Around the hole the lobster has chosen for its home there are hundreds of blooming corals. There’s a bubble-gum pink one that looks like it’s made out of sponges, and a bright magenta coral, home to a cluster of orange fish that don’t seem to be bothered by the lobster’s antennae at all.

Once we’ve all cycled in and out of the best vantage spot for observing the lobster, Derek stations himself in front of it and starts to take photos. He’s so immersed in his photography that Miguel has to tap his carabiner on his air tank to get his attention so that we can move on. The clanging echoes through the water. We keep moving as a group, following Vanessa.

As we round the bend, I pull my focus away from Hugh’s impeccable diving technique – arms locked in front of him, gently kicking, completely at ease – and zero in on the staghorn coral instead. I want to make sure I’ve done everything in my power to do Millie proud.

I don’t see any fish resembling a butterfly wrasse. I see cod, angelfish, parrotfish and gobies, but no wrasse. There’s a cluster of brain coral at the base of the structure that captivates everyone’s attention. Brain coral is mesmerising on its own, it looks like a giant, endless maze, and each ridge is made up of a thousand little polyps, but this coral has an added bonus – above the coral there’s a colony of what look like translucent worms. They are wriggling and every so often catching sunlight. They look like they are dancing. It’s breathtaking.

Vanessa starts kicking and motions to the group to keep moving. Derek, as usual, is still taking photographs. As we pull away from the brain coral, Andrew starts to lose his buoyancy again, this time floating upward with so much speed that Miguel has to grab him and pull him down. Even Natalie is laughing this time, I spot bubbles trailing upwards from her mask.

We swim through a clearing and Vanessa finds a flounder in the bright white sand. I don’t know how she spotted it; it’s so perfectly camouflaged. She pokes at it with her finger and it wriggles and changes colour, flushing from pale white to a light brown with spots. We watch it in wonder as it swims across the ocean floor.