Polar plunge: What it's like to take a dip in Antarctica's freezing waters

It's a marvellous day for a swim. The bay is slick as oiled glass, the sky a spangled dome, the tide a gentle slap on the anchored ship's bow. But the air bites my skin as I slip from my robe and walk past a line of perplexed onlookers; they're swaddled in layer upon layer of polar gear while I'm clad in nothing but a bikini.

The dissonance is overwhelming, and for this you must be prepared. Blue skies and placid waters notwithstanding, it's counterintuitive to swim in the inhumanely cold waters of Antarctica. But it's a rite of passage many travellers can't resist, a physical pursuit with psychological implications. The shock of the cold will cause adrenalin to surge, heart rate to intensify and endorphins to flood your brain, dulling pain and heightening euphoria. So effective is regular cold water swimming, it's being studied as a viable treatment for anxiety and depression.

A clean bill of health is an essential prerequisite for this activity. If you qualify, pack your swimmers and give it no further thought until you're standing by the water's edge preparing to jump in. Brooding on it will only weaken your resolve and trigger the very anxiety you might be hoping to appease. If possible, launch yourself directly into the ocean; a sudden immersion is preferable to the slow, self-inflicted torture of wading into the icy bay from some lonely, stony, guano-smeared shore.

My own polar drenching is instantaneous. Standing on the ship's lower deck, I smile for the cameras, hold my breath – and jump. Frigid water is more fire than ice, so prepare for this bombshell revelation. The water inflames my skin, ravages my nerve-endings, sucks the air from my lungs. I shake myself from the depths, take a pitiful breath, swim back to the ship and haul myself into the plush embrace of a towel held out by a crew member. It's important now to breathe deeply, though one's instinct is to hyperventilate. The endorphins kick in and I laugh maniacally. I'm handed a mug of rum-spiked tea; though my fingers feel cryogenically frozen, I secure my grasp and allow alcohol's thermodynamic properties to soothe me.

The cold-induced high is intense – and so is the tingling in my extremities. Movement and swaddling (socks, gloves, beanie) are essential, despite the positive signals dispatched by those endorphins. Though needles of ice still impale my toes hours later, my soul is positively soaring. A few years later I take the plunge again, on a journey to the Arctic. The shock isn't blunted by prior experience, but nor do I long for warmer climes; where tropical waters once coddled my skin, this subzero swim triggers primordial sensations buried deep within. I'm ravenous anew for the comforts that sustain me, and viscerally alert to the globe's unfathomable extremes.