Somewhere off Sydney’s Northern Beaches, 2006   Easing backwards off the side of the boat, I begin steadily propelling myself down into the depths. The sea takes me into herself and I am free at last to roam this mysterious element that has always felt like home. Despite all the scuba equipment my breathing always feels more relaxed underwater. Suze—that’s my wife—says I must be part amphibian: she also insists I’m getting too old for all this, and my doctor agrees. But when I’m down here I feel no different than I did fifty years ago when I did my…