David Attenborough travels to the ends of the earth on an extraordinary journey across the polar regions of our planet. The Arctic and Antarctic are the greatest and least known wildernesses of all - magical ice worlds inhabited by the most bizarre and hardy creatures on earth. At the North Pole, the sun returns after six months of darkness. A pair of courting polar bears reveal a surprisingly tender side.

After months of darkness the sun returns. The landscape is dynamically transformed, and millions of migrants join the hardy residents as they find mates and begin to breed.

It is high summer in the polar regions, and the sun never sets. Vast hordes of summer visitors cram a lifetime of drama into one long, magical day; they must feed, fight and rear their young in this brief window of plenty. Summer is a tough time for the polar bear family, as their ice world melts away and the cubs take their first swimming lesson.

Polar landscapes in autumn are transformed as the big freeze returns. Most animals leave on epic journeys, some now battle to breed, and for the hardy few it's a time of opportunity. In the Arctic, polar bears gather in large numbers on the coast to wait for the return of the ice. Tempers soon fray and violent contests break out. Off the coast 2,000 beluga whales head for a special estuary, a gigantic `whale spa'.

Winter is the greatest test for life in the polar regions, as temperatures plummet to 70 below and winds reach 200kph. Only a few remarkable survivors gamble on remaining in these extreme conditions. In the Arctic, a female polar bear treks into the mountains to give birth. Out on the frozen ocean, the entire population of the world's spectacled eider ducks braves the winter in a giant ice hole.

Revealing the extraordinary riches and wonders of the polar regions that have kept people visiting them for thousands of years. Today, their survival relies on a combination of ancient wisdom and cutting-edge science. Most Arctic people live in Siberia, either in cities like Norilsk - the coldest city on earth - or out on the tundra, where tribes like the Dogan survive by herding reindeer.