This Week with George Stephanopoulos

Unique insights and sneak peeks are revealed to count down to the toughest survival challenge ever. In-depth looks at 12 of the show's veterans are offered as they prepare to face something twice as hard: 40 days in the Colombian wilderness without food, water and clothing.

Twelve veteran survivalists attempt to survive 40 days and nights in the badlands of Colombia. The heat and lack of water take their toll on the competitors, forcing one to fall terribly ill and another to accidentally slash her finger with a machete. Then, an anaconda threatens to devour one survivalist camping alone next to the river.

After a week of being dropped into the dangerous and desolate badlands of Colombia, dehydration forces one survivalist to tap out. Meanwhile, hunger, thirst and distrust threaten to wreak havoc on several more competitors.

After 14 days in the badlands of Colombia, the remaining survivalists struggle to adapt to their environment and each other. Some consider migrating to try and find new resources, while tension continues to rise in other camps and could lead to the second tap-out of the season.

The remaining survivalists make a desperate trek across the scorching savanna in search of food. If they can't find sustenance, they will be forced to tap out of the most difficult challenge of their lives.

The 10 remaining survivalists reach the 21-day milestone; the group fights for their lives with an electric eel and night visits from a puma.

With 15 days left in the challenge, the dehydrated and protein-starved survivalists converge on a dangerous lake and compete for scarce food and water resources. Tensions rise as one of the groups feels pressured to share their meat with the new, starving neighbors.

After 31 days in the Colombian jungle, the survivalists feel the pressure to get the nourishment they need to survive extraction. However, when one member doesn't play by the rules, the future of one group is threatened.

A duo decides to attempt their extraction alone, causing contention between the teams. Both groups begin their 10-mile journey to the extraction point and must navigate treacherous landscape to try and finish the challenge.

The "Dirty Dozen" survivors come together for the first time since their life-changing, 40-day challenge to discuss the good times, hard time and attempt to heal unresolved issues. They also answer fan questions and unseen moments are revealed.