1. Grand Teton National Park Aaron Huey/ National Geographic Stock Location: 310k acres in northwestern Wyoming.Why you need to go: Don't act like you don't want to see some wild buffalo just casually grazing. Plus, some of the rocks that exist in the park date back nearly 2.7 billion years, and prehistoric species of flora and fauna can still be found there. And with over a thousand campsites, and 200 miles of trails, there's plenty to explore. (Just mind the native grizzly and black bears!) 2. Kings Canyon National Park Rich Reid/ National Geographic Stock Location: Southern Sierra Nevada, east of Fresno, CA. The photo shows the Roaring River Falls against the background of the Grand Sentinel.Why you need to go: Aside from the cool fact that Kings Canyon was carved out by glaciers during the last Ice Age, it's home to huge mountains, deep caves, black bears, and groves of giant sequoia. There's also plenty to do, like camping, horseback riding, skiing, rock climbing, and cave tours. 3. Everglades National Park, Florida. RAUL TOUZON/ National Geographic Stock Location: Florida.Why you need to go: There are mangrove canals for days, like the one pictured, and it's the only place in the world where alligators and crocodiles live together. Alligators and crocs, just killing time together like it's NBD... that's crazy. It's also the largest subtropical wilderness in the United States, and hosts a slew of ways to explore—like airboat rides, biking, canoeing, hiking, tram and guided tours. 4. Yosemite National Park ©Yva Momatiuk and John Eastcott/National Geographic Stock Location: California.Why you need to go: As evidenced by the photo above of Lake Tenaya, Yosemite is known for its spectacular granite cliffs, Giant Sequoia groves, and biological diversity. That's because almost 95% of the park is designated wilderness, making your hike/bike/camping trip blissfully uninterrupted by the outside world. 5. Acadia National Park RAUL TOUZON/ National Geographic Stock Location: More than 47k acres in Maine, which include mountains, an ocean shoreline, woodlands, and lakes. Why you need to go: Ugh, hello gorgeous fall foliage! Because of Acadia's unique landscape, you have the opportunity to take advantage of several different activities; you can swim at the beach, go for a hike, canoe across the lake, or go on one of their guided tours. And while there are snow activities in the winter, you might try to go when it warms up so you can access Cadillac Mountain—the tallest mountain on the eastern coast of America. 6. Gettysburg National Military Park GREG DALE/ National Geographic Stock Location: Just south of historic downtown Gettysburg, Pennsylvania.Why you need to go: This park is a historical gem. You can start your journey in the museum, check out historical artifacts from the Battle of Gettysburg, and continue on by hiking through the trails. A tour with one of their Licensed Battlefield Guide's gives you a history of the spots where you're walking, so you can see the inspiration for Abraham Lincoln's iconic "Gettysburg Address" and feel all sorts of patriotic. Did I mention the colors of the changing leaves?! 7. Carlsbad Caverns National Park Mike Theiss/National Geographic Stock Location: In the Guadalupe Mountains of New Mexico.Why you need to go: Who wouldn't want to see a real-life Fraggle Rock? The limestone formations riddle all of the 118 known caves, and likely began growing during the last ice age. You're free to tour the caves on your own, or take a guided one—try to go between April and October though, so you can see the bats flying around. 8. Canyonlands National Park DESIGN PICS INC/ National Geographic Stock Location: UtahWhy you need to go: Did you know that massive rocks can actually be majestic? Well, they can, and the colorful canyons of Canyonlands proves exactly that. Plus, the remote terrain makes it ideal for hikes, biking, backpacking, four-wheeling, and even kayaking through the Colorado River below. 9. Great Smoky Mountains National Park Michael Melford/ National Geographic Stock Location: This park runs across the border between Tennessee and North Carolina.Why you need to go: This is known as the "wildflower national park," so you can go wildflower spotting, as well as enjoy the plentiful waterfalls. There's also no entry fee to go into the park, which means you can enjoy the 850 miles of trails for free. And if you're a history buff, you should definitely hit up the historical sites, like pioneer log cabins, and archaeological dig sites. 10. Mesa Verde National Park IRA BLOCK/ National Geographic Stock Location: Montezuma County, Colorado.Why you need to go: Do you want to see some 4,000-year-old Pueblo cliff dwellings?! Heck yes, you do, because they're awesome! Mesa Verde was created in 1906 by Teddy Roosevelt and is the largest archaeological preserve in America. Obviously, climbing through the ancient cities is stop number one, but there are also stunning hiking trails and a campground nearby, so you can stargaze at night. 11. Buffalo National River RANDY OLSON/NGS Image Collection Location: Northern ArkansasWhy you need to go: The river, while beautiful to canoe down, isn't the only attraction. The Park is also home to the state's only elk herd, and you can spot them while hiking, biking, or taking advantage of some of the campgrounds. Way to be totally awesome, Arkansas. 12. Shenandoah National Park GREG DALE/ National Geographic Stock Location: The park is part of the Blue Ridge Mountains in Virginia.Why you need to go: There are several waterfalls, hiking trails, and abundant wildlife to be seen—including bobcats and black bears. In fact, the wildlife is so protected in that area that when you camp—in their 196,000 acres—campers have to use "bear bags" to suspend their food from trees, so the bears aren't unintentionally feeding in camp areas. Be beary careful, and get ready for outdoor fun! 13. Wrangell-St. Elias National Park and Preserve Wade Dunkin/National Geographic Stock Location: South central AlaskaWhy you need to go: If you are looking for true solitude with nature, then this is the park to visit. It's the country's largest national park, at 13.2 million acres, and has the biggest collection of glaciers and peaks, including nine of the 16 tallest mountains. Its rugged and wild landscape allows you to hike over glaciers, float across the water, and even spot grizzly bears. 14. Grand Canyon National Park Flickr: grand_canyon_nps Location: ArizonaWhy you need to go: Prepare to be overwhelmed with beauty as you stare at one of the Seven Natural Wonders of the World. Once you're in the park, you can explore the colorful rocks by foot, biking, rafting, and even via a mule ride. 15. Cuyahoga National Park Flickr: 34666709@N00 Location: Northeast OhioWhy you need to go: This park isn't a one trick pony; in the winter you can sled, and when it warms up there's hiking, biking, horseback riding, and even a scenic train ride. They also host a series of concerts in the meadow, and offer an activity called questing—which helps you discover hidden gems throughout the park. Heck, you can even get your fitness on by taking their yoga classes in the park!