Curt and his family have designed a fortress deep in Oregon's back country in the event of an economic collapse.

Former firefighter medics move to the mountains in preparation for a total economic collapse; a man who owns a construction company has built a bunker; a man prepares for a terrorist attack.

Kevin and his family decide to move to Costa Rica because they believe an economic collapse will make America unlivable.

A man who has built spider holes in the Sierra Nevada Mountains to survive the next Great Depression; a family that lives underground in a missile silo bunker.

Mark believes that the U.S. is under threat of foreign occupation; Joe prepares for a cyber attack and builds a post-apocalyptic schoolhouse.

Marine Alex Dunbar trains a private army of German Shepherd attack dogs in San Luis, Colo.; Brenda McSwigan fears that a vicious mutating virus will lead to a pandemic.

Some preppers believe the key to survival is to create a tight-knit community of like-minded individuals.

Prepping for an economic collapse, Jeff is converting a decommissioned missile silo into the perfect bug-out getaway; with an online dating profile, Jeff is also searching for a special someone who can share his love for prepping.

A father prepares his family for dirty bombs; a retired police officer believes that China will bring about economic chaos; a man who has a secret underground hatch in his garage.

Mike and his girlfriend Freda fear that the current political tensions and economic unrest will lead to a world war; Mike Adams is anticipating a terrorist attack; Joe, has given up on modern living.

A man prepares his family for an electromagnetic pulse attack; a New York firefighter prepares for the eruption of the Yellowstone super volcano.

A man fears the economy's collapse and has built a bug-out dome in the wilderness for his family, accessible only by boat; a man from Hawaii who fears a catastrophic tsunami will strike the islands.

Would an explosion on the surface of the sun cause mayhem on Earth? Jason and Jacob are a father-son team from Alabama who are prepping for a global solar flare with the potential to wipe out power grids around the world and is prepping in the woods by molding his own ammunition and preparing his 20-piece bug-out pack. In Arizona, the Moffatt family prepare their seven children.

Some preppers like Jeff Mann believe in safety in numbers, while others like Tony, who believe that an end of days asteroid will turn the Earth into ash, are independent.

A woman creates a gourmet meal using only shelf-stable foods; a man who has trained his children to withstand a financial collapse.

A woman who fears a catastrophic New York City hurricane; a college student prepares for the meltdown of the Indian Point nuclear power plant; a bond trader fears a terrorist attack in the form of a dirty bomb.

A man who fears a terrorist attack on nuclear power plants; a farming family prepares for a series of F-5 tornados; a couple fear the melting of the Greenland ice sheet.

Chad believes that a nuclear strike resulting in a genocidal siege is a real possibility. He is working on executing an escape tunnel from his family's house to a vehicle.

Brian smith prepares for collapse of U.S. monetary system and fears the world's food supply will dry up.

Kenny and his wife are preparing for a civil war with a fortified bulletproof rooftop command center; Kevin is prepping for an EMP attack by building an underground bunker.

Two families who fear the end of the world is coming are preparing for Category 5 hurricanes and a complete economic collapse.

The old Dolly Parton hit "9 to 5" isn't a tune worth humming for the blue-collar pioneers featured in "Filthy Riches." The series spotlights ingenious Americans who skirt a conventional workplace in favor of making a living in the deep rivers, soggy mud flats and wild backwoods of the U.S. Ray Turner, for example, has been catching eels in Delaware for 30 years. He uses a self-made smokehouse in the woods to cook the critters and sell them. Billy Taylor and his sons hunt for prized ginseng root in the Appalachians. Taylor, a fully licensed wild ginseng dealer, promotes sustainability by planting its berries. In Maine, Jim Campbell and Andy Johns make the coastal mud flats their office, as they dig for valuable bloodworms to sell to fishermen. And Greg Dahl and Albert DeSilva are burl hunters. A burl is a hard, unwieldy outgrowth on a tree, usually at the trunk. Burls have value because of the spectacular patterns found in them when cut open.

When bears, wolves and foxes are your only neighbors, life can be pretty lonely. Add minus-60-degree days and a constant battle for the most basic necessities, and you have the daily challenges of people who live in remote corners of Alaska. This series takes viewers deep into an Alaskan winter to meet tough, resilient residents as they try to stay one step ahead of storms and man-eating beasts to survive the season. The closest neighbor to Sue Aikens is more than 300 miles away. Eric Salitan subsists solely on what he hunts and forages. Chip and Agnes Hailstone catch fish for currency in bartering for supplies, and Andy and Kate Bassich use their pack of sled dogs for transportation. Also highlighted is a time of year not always part of what viewers see in Alaska: spring! Ice is breaking, animals are waking, and residents face new tests before deep cold returns.

Mick Dodge is one with the woods, having left modern conveniences behind 25 years ago to live among the trees, caves and animals in Washington state's Hoh Rain Forest. It's not an easy life by any means -- he sleeps in tree stumps and has no easy access to food -- but each day presents a different adventure, and as the always-barefoot Dodge says, "All I have to do is follow my feet." He's walking in the footsteps of four generations of Dodge men who have called the Olympic Peninsula their home, and because the intensely private former Marine allowed National Geographic access to his world, this time viewers are welcomed to witness the primal life of "The Forrest Gump of Middle Earth."

TV's most extreme survival challenge just grew extra-large. Veteran survivalists familiar with the stripped-down drill after appearing on "Naked and Afraid" attempt to survive in a desolate, dangerous environment for 40 days -- 19 more than they previously experienced on the show. Pushing the very limits of human endurance, the men and women must all vie for the same limited food, water and shelter while avoiding territorial-sensitive predators and venom-filled reptiles. Because there is no other choice, the competitors quickly get to know one another -- and their surroundings -- and hope that their instincts, survival skills and intestinal fortitude serve them well.

Extreme survivalists go head to head in a race across the Alaska wild. Using ingenuity, experience and just the gear they can carry in their packs, the participants have 60 hours to reach the finish point of each leg of the adventure -- the series features 13 legs -- and in addition to navigating treacherous glaciated river valleys, barren ridgelines, and high mountain peaks, the challengers battle hunger, dangerous predators and unpredictable weather. There is no grand prize awaiting each leg's winner, other than the pride of accomplishing a grueling feat. For season three, the 12 competitors are divided equally into four teams -- Military, Endurance, Alaskans and Lower 48.

Back to the beautiful state of Alaska for another reality-documentary series, this one set in the Arctic National Wildlife Refuge, a protected area home to thousands of native animals... and a handful of people. In 1980, the U.S. government banned human occupation in the refuge, and only residents in seven permitted cabins are allowed to remain. The series depicts the daily rituals of four families living in isolation and contending with bitter weather, frustrating setbacks, and aggressive wildlife in an unspoiled and unforgiving wilderness. The nonconformists include Heimo Korth, the "godfather of the final frontier," and wife Edna; Bob Harte, who has spent 40 years living by his own rules; and young couple Bob and Ashley Selden, who admit that they've survived by trial and error, learning day by day the harsh reality of frontier living.

Each year adventurers make Alaska's mighty Yukon River their home for five weeks. They float downstream on homemade log rafts to sell firewood and other supplies to remote villages. The reality-documentary "Yukon River Run" presents hourlong episodes tracking the progress of various crews. As harsh winter months approach and threaten both safety and success, stakes are heightened as rafters endeavor to cash out and escape from the cold.

Discovery Channel takes the ubiquitous survival show theme to the next level by stripping it to its bare essentials. In "Naked and Afraid," complete strangers -- usually a man and a woman -- meet in a very unique way: They're stranded in a dangerous, desolate location, without food or water, and they're completely naked. Each episode follows the adventurers as they attempt to survive on their own with nothing but a personal item and the knowledge that the only prize is their pride and sense of accomplishment. Because there is no other choice, competitors quickly get to know one another -- and their surroundings -- and hope that their instincts, survival skills and intestinal fortitude serve them well.

Academy Award winner Morgan Freeman explores the meaning of life, God, and many big questions in between in an effort to understand how religion has evolved and shaped society. A different divine subject is covered in each hourlong episode, titles of which include "Creation," "The Devil Inside," "Afterlife," "Apocalypse," and "Who Is God?" To explore these topics, host and narrator Freeman visits nearly 20 cities in seven countries to see some of the world's greatest religious sites, among them Jerusalem's Wailing Wall, India's Bodhi Tree, Mayan temples in Guatemala, and the pyramids of Egypt, and he immerses himself in religious experiences and rituals. "In some places I found answers, and others led to more questions. The constant through it all is that we're all looking to be part of something bigger than us. If there's one thing I've learned, it's that we certainly are," Freeman says.