The coastline south of Hobart on this soft spring afternoon is as sweet as it’s ever been but the water, at 15 degrees, is more provoking than inviting. After a spell in a Finnish-style sauna heated to 80 degrees – a floating sauna, to be precise – I approach the challenge in a lather of sweat. As I stand on the deck, swinging my arms and summoning my nerve, a phrase from an old World War II submarine movie comes to me unbidden: “Prepare to dive!”

I carve into the gelid depths to the sound of an effervescent swoosh, though I feel nothing (but shock and numbness). Seconds later a delicious chill sweeps across my skin and I’m laughing like a mad thing. It’s then that the biting cold, along with the instinct to flee, kicks in. Grimacing, I swim back to the sauna boat and return to my wooden bench beside the hot coals.