Tioga Pass and Yosemite's Highway 120 are known for their stunning scenery and unrivaled access to the High Sierra. Discover how and why this historic road came to be.

Ketchikan is a gateway to southern Alaska's wild outdoors! The area is filled with dense woods, abundant wildlife and adventure around every corner but it is also a place where the weather doesn't always cooperate -- as Greg soon discovered. Greg explored Ketchikan with two very enthusiastic guest hikers  Nina and Carey.

It's one of America's iconic national parks, best known for its towering granite cliffs and spectacular waterfalls. But even though nearly four million people a year visit Yosemite National Park in California, few have ever seen this remote section of Yosemite hidden deep in the high peaks of the Sierra Nevada Mountains. Greg embarks on a rugged journey into a region of the park few people ever see. The alpine landscape here is breathtaking, and also treacherous. Focus and preparation are key to a safe and successful trip.

On the border of the Inyo National Forest and Yosemite National Park, lies one of the most prominent mountains found in the Sierra Nevada Mountains--Mt. Conness. It's a diverse and challenging mountain to climb as Greg and the guest-hikers are about to find out. With the help of Ian Elman of Southern Yosemite Mountain Guides, they hope to summit this iconic peak!

Saguaro National Park is named after the giant species of cactus it was originally established to protect. It is now one of the largest preserves in the United States for this iconic symbol of the American west. It is split into two separate regions -- called districts -- on either side of Tucson, Arizona. Each district is on the outskirts of town, making this an easy park to access from a major metropolitan area. Kristi and Ray from San Francisco joined Greg on this trip. This was their first trip to the desert.

San Francisco is a fast-paced city on the California coast in the second-most densely populated metropolis in America, but just minutes away, you can lose yourself in the wild solitude that is worlds away from the pulse of city life.

Greg and two guest-hikers travel to the dense jungles of Costa Rica and discover a rarely seen tropical paradise. Two national parks are explored by river through some of the thickest jungles in Central America.

It's a wide open and barren desert landscape, but a closer look reveals the unique wilds of California's largest state park. From caves sculpted by wind to a true desert oasis that took us all by surprise, this is another Southwest destination big on scenic beauty. Greg invited two guest hikers for the journey to Anza Borrego. Michael Roeshman, a battalion chief with the Philadelphia Fire Department and Captain Eric Snyder, also a member of the PFD.

Valley of Fire State Park's stunning red rocks and bright blue skies set the stage for an outdoor destination that is tough to beat. But these hidden canyons and sandstone caves are relatively unknown because they are overshadowed by the bright lights of nearby Las Vegas, Nevada. Greg Aiello brought along regular Las Vegas visitor, Dave Denny, who never knew there so many unique places to explore in the area.

Without a film crew, Greg Aiello embarks on a solo 11-mile climb up the Kalalau Trail, a treacherous hike attempted by few tourists who visit the Hawaiian Island of Kauai. His path leads directly past gorgeous views from sea cliffs of the Napali Coast.

Greg Aiello kayaks through Costa Rica's Tortuguero National Park where he gets a close look at the jungle's wildlife. Melissa and Matt joined Greg on this adventure in Costa Rica. The couple lives on a farm in southern New Jersey.

Northern California's Redwood National Park is a dense forest home to the tallest trees on earth. But it is a place also known for its diversity where hikes through enchanting settings lead straight to the sea. Greg invited a guest hiker to explore the park with him. Mike from Long Island, New York, has never seen anything like the redwood giants before.

Somewhere not so far removed from the bright lights and the glitz of the Vegas Strip lies one of southern Nevada's best kept outdoor recreation secrets -- Red Rock Canyon National Conservation Area.

Lake Ouachita is the largest lake in Arkansas. It is surrounded by undeveloped shores and is a paradise for boating and fishing. With some of the cleanest waters in America, this is a summer vacation destination that is really tough to beat.

Mesa Verde National Park in Colorado is home to the largest archeological preserve in America. You can find the remains of a lost civilization hidden in the walls of park's canyons. These mysterious dwellings still hold many secrets and the thrill of discovery for those ready for a unique adventure. Greg set out to explore the park with Britt and Mike -- an active couple from Chicago who love the outdoors. They are both avid cyclist.

Interior Alaska is one of the last great frontiers in the world and home to one of the most stunning national parks in America. It is the perfect place to truly get away and start an adventure in an incredible place. Greg invited three of his old friends to explore Denali National Park and Preserve with him.