In the fourth episode of the series, legendary nature and cultural photographer Art Wolfe captures the great brown bear with the stunning backdrop of Alaska’s mountains and glaciers, immigrating wildebeests in the plains East Africa, and the hard-to-find gorillas of Uganda.

Every year, over a thousand climbers try to reach the summit of Mount Everest, with the annual record for successful attempts currently standing at 633. But of that number, nearly half were Sherpas - the mountain's unsung heroes. Yet the Sherpa community has remained secretive about their nation, culture and experiences living in the shadow of the world's highest mountain. Now, for the first time, they open the door into their world. Without the expertise of the Sherpas, only the hardiest and most skilful climbers would succeed. Every day they risk their lives for the safety of others, yet they seek neither glory nor reward, preferring to stay in the background. Following the stories of four such Sherpas - Phurba, Ngima, Ngima Tenji and Gelu - this film reveals the reality of their daily lives, not just up the mountain, but with their families after they return home.

On a vast plateau cradled in the heart of the rocky mountain range lies two million acres of unspoiled wilderness, never farmed and never fenced. Canyons, lakes, rivers and mountains, a refuge for magnificent animals and a spiritual sanctuary for generations of Americans, all resting on the largest super volcano in North America. This is Yellowstone, America's first national park, a raw and powerful beauty that truly comes to life through immersive 3D.

On a trip to the fortified Moroccan village of Ait-Ben-Haddou in the Atlas Mountains, Professor Brian Cox reveals how by watching the stars' motion across the night sky, it is quite natural for man to think he is at the centre of everything. That view was held for many ages, but innate human curiosity has eventually led to an understanding of mankind's true place in space and time, and an appreciation that Earth is not a focal point but a mere particle of rock in a possibly infinite expanse of space, 13.8 billion years from the beginning of the universe.

Enjoy this wonderful documentary from Disney Nature about a family of brown bears living in the coastal mountain ranges of Alaska." A brown bear mother named Sky gives birth to two cubs named Amber and Scout in her den on a mountain slope. When April comes the bears will be ready to leave the den. As the bears leave the oncoming summer brings with it a threat of avalanches. Fortunately the bears are able to avoid disaster. Upon reaching the lush valley below, the cubs meet the other bears, some of which pose a threat to the cubs; among these bears are Magnus, a big healthy male, and Chinook, an older male. The family works together to survive the spring, with Sky keeping the cubs safe from Tikaani, a pesky grey wolf...

A group of brave individuals risk their lives to save the last of the world's mountain gorillas; in the midst of renewed civil war and a scramble for Congo's natural resources." Virunga National Park in the Congo is a place of unique natural beauty. It is the home to a plethora of wonderful animals and vegetation but as is so often the way, it has several serious problems that threaten it. It's the location of human violence, corruption and exploitation. The disasters that specifically loom are two different groups, the M23 and SOCO International. The former are a violent rebel force who engages in an ongoing civil war with the Congolese government and the latter are a British energy company who specialise in oil exploration. Both M23 and SOCO invade the park in their own ways and neither seems very interested in the laws that have been set up to protect the flora and fauna that exist there, far less the people who live there. It seems hardly surprising in the case of M23, as they are a paramilitary organisation who can hardly be expected to be concerned with such things but it is the more legitimate big business SOCO who seem more worrying if anything. We discover in fact that they have been involved in a bribery campaign, utilising M23 as enforcers. It's a very murky situation where big money walks all over an impoverished nation and disregards a natural space that they can see no value in in their pursuit of financial profit.