Fort Knox: Discover the secret contents, political controversy and cutting-edge security lurking behind the gates of the most famous vault in the world, Fort Knox. (S1, ep 3)

The Ku Klux Klan: Former Ku Klux Klan leader Johnny Lee Clary shares the secrets of the Hooded Order, including the extent of its power and its secret greetings and goals. (S2, ep 2)

Freemasons: Unlock the mystery surrounding the hugely secretive and powerful brotherhood and discover the truth about their vision, meetings, symbology and bizarre rituals. (2 of 10)

Scientology: Former scientologists reveal what drew them to the church and why they chose to leave. An eye-opening look into the mysteries and allure of Scientology. (S3, ep 1)

The Ancient Astronaut Cover-Up: Apollo 14 astronaut Edgar Mitchell is among the experts discussing the possibility that aliens have been visiting the Earth for centuries. (S2, ep 1)

Rain of Terror: An experiment with new food backfires as one survivalist becomes violently ill. As the rain persists, the men question whether they can continue. (S1, ep 5)

Winds Of Hell: A storm shakes the island, leaving the men battling to protect their shelters and close to cracking. One contestant takes to the choppy sea in search of food. (S1, ep 5)

Stalked: One of the contestants falls ill and begins to question his grip on reality. Eager to reap the rewards of a salmon river, another survivalist puts his life at risk. (S1, ep 4)

Talons Of Fear: As the effects of isolation start to set in, a careless mistake puts one man in grave danger. Another gets trapped in a terrifying situation with a predator. (S1, ep 3)

Of Wolf And Man: A desperate hunt for clean water sends one survivalist on a perilous mission. Bears and wolves stalk many of the other men who are alone in the wilderness. (S1, ep 2)