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David Attenborough reveals the extraordinary ways in which animals battle to survive the elements in a world of extremes - places where life exists on a knife edge. From mountain summits to scorching deserts, polar tundra to deep underground caves, these remote places are rarely visited, yet the animals that survive there are some of the most resilient and specially adapted on Earth.

In Vietnam, the true scale and grandeur of what’s thought to be the world’s largest cave - Hang Son Doong - is revealed. In its depths, blind, white cave fish are found in tiny pools of water, surviving on nutrients washed in from the jungle above.

On Ellesmere Island, a pack of Arctic wolves fight to rebuild their strength after one of the toughest winters on earth. But the season of plenty is not all it seems – with prey so scarce they must travel vast distances to find it. And when they do, they must battle their ancient foes - musk ox, a relic of the Ice Age. The wolves’ success during the short Arctic summer could mean the difference between life and death.

Emerging after months below the ice, a European common frog sticks his head out of the snow. It’s a sunny Spring Day in the Alps - the perfect day to find a mate. But he’s not the only one – dozens of other frogs are all making their way to the breeding pool. It’s a race to get there before the other males. Will he get there in time?

Huddling can be a survival superpower, especially in the winter cold of the Atlas Mountains. For a young Barbary macaque, separated from the group, it’s vital to find and re-join the huddle before nightfall… but there is a surprising obstacle in his way.

Possibly the ultimate huddle is found in the mountains of Mexico, where millions of monarch butterflies are overwintering. But the calm is shattered when a storm hits their forest shelter.

Fires are one of nature’s most destructive forces, but they are also vital for keeping some habitats healthy - few places more so than northern Australia’s savannahs. A pair of golden-shouldered parrots are raising their family inside a termite mound! Thick walls keep the chicks safe from predators, but when a fire unexpectedly strikes, will the nest protect them?

As the climate changes, extreme weather events are becoming more frequent and often more intense. On the plains of Kenya, an elephant matriarch is struggling to keep her two sons alive. After months of drought and with food and water supplies critically low, the family are faced with tragedy.

Few places are more extreme than the Gobi Desert - temperatures here can range up to 40 degrees Celsius. But one iconic animal of the extremes has made its home here: the snow leopard. This rare and intimate view of a mother and cubs reminds us that the extremes still hold some of planet earth’s greatest secrets and most spectacular natural wonders.