Will heads to the South Pole, where temperatures can drop below minus 100 degrees Fahrenheit. He skis and treks across giant icefields, and, faced with a giant cliff of ice in bone-chilling winds, struggles to climb to the top. Only with the support of one of the world’s best polar athletes, Richard Parks, does he succeed. In one of the planet’s most isolated research stations, scientists take ice cores deep under the surface and make incredible sacrifices to pursue their research.

Will, a man scared of spiders his whole life, ventures deep into the Ecuadorian Amazon on an expedition in search of deadly creatures. Joined by professor Bryan Fry and local mountaineer Carla Perez, they abseil 200 feet into a cave network known as the “womb of the Earth,” where they discover a giant tarantula. Using cutting-edge techniques, they extract its venom, which could hold the key to saving millions of lives.

Will, Bryan and Carla join local Waorani elder Penti Baihua in the Amazon, in search of the world's biggest snake: the giant green anaconda. They carefully remove just one scale from the 17-foot snake’s skin. Will’s fear turns into relief, then joy. The single scale can reveal the health of the entire ecosystem — crucial for the future of both wildlife and the Waorani.

Will travels to the kingdom of Bhutan on a deeply intimate journey in search of the secret to happiness. Guided by happiness expert professor Dacher Keltner and local writer Tshering Denkar, Will treks to one of the highest and happiest villages in the Himalayas, at 13,000-foot altitude. While there, he confronts some of the most challenging moments of his extraordinary life and career.

Joined by linguist Dr. Mary Walworth and local marine ecologist John Aini, Will travels to the South Pacific on an expedition to a remote island threatened by rising seas. What begins as an exploration into an incredible marine paradise transforms into a truly revelatory journey for Will about his own history as they record a lost language spoken by only five people.

Will travels deep into the Kalahari Desert to meet the San people, one of the oldest hunter-gatherer groups on Earth. To discover the secret to their enduring success, he must join them on a hunt in one of the most inhospitable places on the planet. Led by local San bushman guide Kane Motswana, it’s not long before he realizes he’s entirely unsuited to this adventure.

The final leg of Will’s 100-day adventure is his most dangerous mission yet: an expedition to dive under the ice at the North Pole to help polar ecologist Allison Fong capture world-first scientific samples. But when a snowstorm and mechanical failure put the mission in crisis, Will learns what it takes to be a hero in real life.