I've just discovered it on holiday in Turkey. The thrill is tremendous, five whole metres down, feeding fish and doing frantic hand signals. There's a lot to learn. Thumbs up means: "I'm drowning, I want to come up." Pointing to your ear and doing a wobbly, lateral, iffy sort of movement with your hand means: "My eardrum is about to burst." Swallow, they tell you. But how, when I've no spit to swallow with? you signal back.
But to teach it! That must be a greater thrill. People's lives are in your hands, not just exam results and careers. In that great subterranean classroom the whole of the Med is waiting to rush into their mouths. It really means something when you say "listen up". If they don't they'll drown.
And on the boat going out, there's 40 minutes to spend lecturing a captive, scared audience. It's teaching at its sadistic best. Like invigilating a particularly nasty exam where students who haven't worked all year are paying for it now. Or collecting coursework and smiling at the ones who haven't done it. "Never mind," you tell them, "it's too late now," then making some cruel, sarcastic joke.
It's power. Yes, I'd like to teach under the sea. And why stop there? Free-fall parachute-jumping, hang-gliding, lion-taming - there are far more interesting subjects than English.
There is just one snag. I did indeed scuba dive - once. But badly. I scuttered along the bottom, unable to fin my way through the water in a galaxy of bubbles like everyone else. But that's not the point. I want to teach it. Not do it.
Richard Hoyes teaches at Farnham College in Surrey.