From the door of our caravan, I can see the ocean breathing. Its blue chest rises and falls to wash on to the rock shelf below us. It is loud, the waves sound like the rush of wind gathered by a road train as it roars past you standing, insignificant and tiny, on the side of the road. The feel of their power is the same. Each breath fades quickly, only to be replaced by another thunderous explosion as the swell delivers its energy bomb to the land. The shorebreak is monstrous, 8ft of perfect, terrifying curl collapsing all at once and washing meters up the beach.

The boys are having a terrific time, daring the sea, being slid up the beach on their bottoms in the foam, coming out covered in sand.

Its not always like this though. Last week there was no swell. The ocean was flat, approachable and we woke up on Wednesday morning to see 4 big Manta Rays, idly flapping and cruising just off the rock shelf in front of our camp. We watched them for ages, until I saw a family in snorkel gear stride purposefully to the edge of the shelf, and hop in.

There were no waves to stop us today, but it was still a leap of faith to don snorkels and jump in to the sharky waters. To be honest, if it hadn't been for that first family, I would not have even considered going in. What a rare gift though, a chance to swim with this most elegant of creatures in the clearest, bluest, most untouristed environment imaginable.

Under the water, the ledge jutted out to form a watery canyon whose sides dropped vertically to the rocky sea floor. Large schools of trevally hung around the overhangs, and clouds of buttercup yellow parrotfish drifted past. Then a Manta appeared, silently materialising out of the gloom of the deeper water, its big mouth open to scoop up invisible morsels, weaving around us in graceful, banking arcs. Black and velvety on top, it was bone white unerneath.

Oscar, Ned and I swam and dived again and again to experience the pure joy of existing in this crystalline paradise with such fish. It left us for bubbles, however, disappearing back in to the deeper water.

Several more Rays came over to dance with us, and I think our experience was heightened by the frission of danger every time we strayed close to the deeper water. This was raw nature, anything could come out of that gloom. Simply snorkelling off the shelf was an achievement for us all and when I finally got out, I practically pushed Tom in so that he could experience it too.

The whole experience reminded me of a recurring dream that I used to have when I was younger. I would jump off the cliff in my old summer haunt in Cornwall and sink to the bottom of the sea. In my dream, I could breathe underwater and the sea was crystal clear and there were all sorts of exotic, colourful fish. I would spend the whole night swimming underwater through this world and wake in the morning feeling rapt. I had that same rapture when I dived with the Mantas and I wanted to stay under the water for far longer than my lungs were up for.

Once I had levered the boys out on to the shelf ( no easy feat when the rocks are bristling with sea urchins), I went back out with Tom for a last dance.

It is possible to swim with Mantas all along the Coral Coast. The last tour I saw in Coral Bay cost $250. I seriously considered going as I thought it would be my last opportunity, but we simply could not afford it. So to have this spontaneous, natural swim was extraordinary and proof for me, that the Universe works in mysterious ways.