Russians have only two words for cold or, at least, that's what I was told. I don't think that's enough. If you're diving beneath the ice for any length of time, you start to distinguish between the different sensations produced by the low temperatures. There's the painful cold you feel when you first put your face in the icy water, like pin-pricks all over your bare, exposed skin; there's the numbness when you've been immersed for 40 minutes and can't feel your hands and feet; there's the bitter chill from the wind when you're outside in 10°C in the wind and snow tending a rope that disappears into the ice; and there's the deep-down cold in your bones when you can't get dry or warm after a dive, your body starts to shut down and all you want to do is sleep. Am I painting an attractive picture?

While the rest of the world is just discovering that diving under ice-covered lakes can be fun, a bright young Russian marine biologist is already leading teams to the White Sea, the North Pole and Antarctica. Ice diving is dangerous, expensive, complicated, unprofitable and uncomfortable, and even less popular than cave diving. So why is he devoting his life to pioneering it? Because he loves what can be found only under ice: the clear water and the fantastic, infinitely varied shapes of the ice itself; the violent mating of the giant snow crabs, the delicate combfish that float by and, in lakes, teasing crawfish and catching sleepy fish by hand. And some day, so will we.

I met Mikhail Safonov at the North Pole in 1999. The previous year, a professional rescuer, Andrei Rozhkov, had approached him about organizing the first spring dive at the pole. They would take advantage of a temporary base (set up for skiers, balloonists and parachutists each April since 1994) to bring their equipment and get a helicopter ride to the exact pole. Rozhkov, a veteran parachutist and diver, had died of a heart attack during the dive, and I had been two miles away, on an expedition of my own. The first man to dive at the pole had become the first man to die there.