E.J. and Jeff are trapped in a pitch-black cavern surrounded by bears.

E.J. and Jeff are surrounded by lions on South Africa’s Wild Coast.

E.J. and Jeff face elephants and hippos in Botswana's Okavango Delta.

Primitive survival expert Matt Graham demonstrates how to build an atlatl.

Primitive survival expert Matt Graham demonstrates how to build a fire.

Survival expert Matt Graham demonstrates how to purify drinking water.

Primitive survival expert Matt Graham builds a lookout from a small tree.

Primitive survival expert Matt Graham demonstrates how to fell a tree.

Primitive survival expert Matt Graham demonstrates how to build a smoker.

Primitive survival expert Matt Graham demonstrates how to build a shelter.

Primitive survival expert Matt Graham makes a bucket out of tree bark.

Primitive survival expert Matt Graham demonstrates how to make a bow drill.

Primitive survival expert Matt Graham demonstrates how to make a blowgun.

Seven people with superhuman skills take on a brutal obstacle course.

Two super fans train before attempting a full 21-day challenge.

Two sets of identical twins are dropped in the African savanna.