Some people might only dream of adventure, but for others, there’s no other option but to explore the most extreme places on Earth. From the deepest caves to rough oceans, from the North Pole to dizzying heights on a high wire  — what drives adventurers to constantly push to the brink of human endurance? In this hour, TED speakers share their experiences of going to the edge of our world.

1. Ben Saunders: What’s It Take To Become A Polar Explorer?

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2. Bill Stone: Are Earth’s Deepest Caves The Last Frontier?

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3. Roz Savage: Why Row Across The Oceans?

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4. Philippe Petit: Why Is The High Wire Impossible To Resist?

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