The national parks of the United States are a treasure -- beautiful, wild and full of wonders to see. No wonder so many people travel great distances to enjoy them. But there's more to experience than taking in gorgeous scenery from your vehicle or lookout points. These are natural playgrounds, full of possible adventures. The most famous offerings of the National Park Service are the 61 headliner national parks, including Yellowstone, Yosemite and Grand Canyon. But there are actually 419 National Park Service sites across the country, often called "parks," but they include those national parks, seashores, lakeshores, battlefields and more. So we're going to kick it up a notch (or two) and look at some of the more adventurous activities you can enjoy in places run by the National Park Service and pair them up with superb parks for the experience:

Hiking

The Narrows at Zion National Park (Utah) It's hard to find a national park that doesn't have some good hiking opportunities, but The Narrows at Zion National Park take adventurous hiking to a new level. Why is it so memorable? First of all, you're hiking through a cold, shallow river, the Virgin. (There might be times of the year, such as early spring, when the trail is closed because of high water. And always check the weather forecast -- flash floods are real danger here.) And then you're hiking through canyon walls that can be up to 1,000 feet high (309 meters) but only 20 to 30 feet wide in spots. Definitely chilling and thrilling. Two other adventurous options: Olympic National Park (Washington): See everything from craggy, snow-covered peaks to a bona fide rain forest. Hawaii Volcanoes National Park: The name of the park says it all -- volcanoes!

Bicycling

Acadia National Park (Maine) Steep, winding carriage roads in Acadia National Park can provide excitement, heart-pumping exercise -- and some of the most stunning views in the eastern half of the United States. The ride up Cadillac Mountain can be especially challenging but also so rewarding. Two other adventurous options: Glacier National Park (Montana): You'd be better fit to take on Logan Pass, but your prize is a look at glaciers that probably will be gone in coming decades. Canyonlands National Park (Utah): This is an ideal park for long mountain bike trips on rugged, four-wheel-drive roads.

Swimming

Trunk Bay, Virgin Islands National Park (St. John, US Virgin Islands) Put on your swimming trunks and head to Trunk Bay at Virgin Islands National Park. Shutterstock Indulge in one of the most beautiful beaches in the world -- swimming at Trunk Bay in Virgin Islands National Park will be one of the highlights of your life aquatic. While the swimming itself isn't particularly challenging here, the surroundings elevate this beach to a top pick. Rent some snorkelling gear for an even better look at sea life on a marked underwater trail. The area took a hard hit 2017 hurricane season but is in recovery and definitely open to visitors. Two other adventurous options: Little River Canyon National Preserve (Alabama): Swim in natural pools surrounded by boulders and small rapids. Getting down the canyon's steep banks to the river is half the adventure. O'heo Gulch, Haleakalā National Park (Maui, Hawaii): Sometimes called the Seven Sacred Pools, there are actually dozens of waterfalls/pools for you to swim in when the water's up.

Beach exploration

Point Reyes National Seashore (California) This is for folks who want more out of a beach than a smooth patch of sand to spread out a blanket, calm waters for wading and lots of social interaction. The beaches at Point Reyes are for hardy adventurers who enjoy pounding surf, animal sightings and stunning vistas from craggy cliffs of unspoiled shores. And depending on when you go, you might not have to share the experience with a bunch of other people. Bonus: This wild and beautiful part of the Pacific Coast is easy driving distance from urbane San Francisco. Two other adventurous options: Cape Cod National Seashore (Massachusetts): This spot on the Atlantic got a 1800s endorsement from Henry David Thoreau of "On Walden Pond" fame: "A man may stand there and put all America behind him." Gulf Islands National Seashore (Florida and Mississippi): This bisected park on the Gulf of Mexico is gorgeous and has plenty of things to keep you active -- biking, bird watching, fishing and more. And yes, if you do want to just stretch out and enjoy the view, you can that, too.

Horseback riding

Rocky Mountain National Park (Colorado) It's the ultimate dream for horse lovers -- saddling up for some trail riding out West with gorgeous mountains as a backdrop. You'll find it all at Rocky Mountain National Park. See snow-capped peaks and alpine lakes and perhaps spot bighorn sheep and elk as you ride. In addition to horses, the park allows mules, ponies, llamas and burros on roughly 260 miles of trails.  Two other adventurous options: Great Smoky Mountains National Park (Eastern Tennessee and Western North Carolina): Take guided horseback rides from mid-March through late November. Or bring your own to explore 550 miles of trails. Theodore Roosevelt National Park (North Dakota): If it's named after our rough 'n' tumble 26th president, you know it has to be an adventure. Find out why the Badlands are so good for riders.

Camping

Denali National Park (Alaska) Camping at Denali is always an adventure -- especially if you see the northern lights at night. Kent Miller/NPS Photo Why not go big when you go camping at one of the most remote and wildest of the national parks, Denali? Set up a tent and sleep under Alaskan stars with bears, wolves, moose and eagles. And your heavenly bonus if you're willing to brave the colder weather of fall, winter and early spring: a decent chance of catching the spectacular northern lights. Two other adventurous options: Assateague Island National Seashore (Maryland and Virginia): Camp on the beach of this barrier island famed for its wild horses. (Camping available only on the Maryland side). Voyageurs National Park (Minnesota): When you're craving isolation, head to this park in the wilds of northern Minnesota.

Wildlife encounters

Yellowstone National Park (Wyoming, Montana, Idaho) When you think "national park," you probably picture Yellowstone. And there's no denying the spectacular, wild menagerie that awaits you at the granddaddy of national parks. What animals might you spot here? Grizzly bears, black bears, bison, elk, mule deer, wolves and cougars all call the park home. And it's not just big mammals. You might glimpse playful otters, long-tailed weasels and smaller mammals. As for the birds, there's a wide range -- from raptors such as bald eagles and falcons to songbirds and woodpeckers. Two other adventurous options: Saguaro National Park (Arizona): Head to the desert to witness creatures such as jackrabbits, bobcats, javelina (similar to wild boars), gila monsters, rattlesnakes, owls and hummingbirds. Glacier Bay National Park and Preserve (Alaska): This is the park for you oceanic types. Possible sightings: Humpback whales, harbour seals, porpoises and sea lions.

Scuba diving and snorkelling

Channel Islands National Park (California) For one of the most unusual scuba dives you'll take, submerge yourself in the otherworldly kelp forests of Channel Islands National Park. Here, the plants steal the show from the animals. These kelp forests, which attach themselves to rocky reefs, indeed resemble trees and attract an abundance of fish. And if you're not certified for diving, try snorkelling in places such as Anacapa Island, which usually has good visibility. Two other adventurous options: Dry Tortugas National Park (Florida): Go diving and snorkelling in a park that's 70 more miles west from an already isolated Key West. See some of the most vibrant coral reefs in the continental United States. War in the Pacific National Historical Park (Guam): If you love history and scuba diving, find a way to get to this US territory way, way out in the Pacific The wreck diving here is amazing.

White-water rafting

Grand Canyon National Park (Arizona) Do you have what it takes to challenge the Colorado River in the Grand Canyon? NPS Photo Hey, if the Colorado River is powerful enough the carve the Grand Canyon, it ought to provide you with some of the most thrilling white-water rafting of your life. And it has it all -- from smooth runs to Class 5 rapids. You can choose from commercial trips as short as a half-day to noncommercial outings last weeks. The park's rafting page on its website provides you with all the possible trips you can take. Two other adventurous options: Dinosaur National Monument (Colorado and Utah): Take on the challenges of the Green and Yampa rivers, which test the mettle of even experienced boaters, to see this area's remote canyons. Big Bend National Park (Texas): Float past canyon walls that are 1,500 feet high and take on the thrills of the Lower Canyons where you may encounter Class 4 rapids. And you get to traverse an international border with Mexico.

Rock climbing

Joshua Tree National Park (California) Better known for its cacti where two distinctive desert types meet, Joshua Tree is also a superb place to do some rock climbing. The park has more than 8,000 climbing routes and has the distinction of being a great place to go bouldering as well. Be sure to read up on the park's safety guidelines before you begin your steep adventures. Two other adventurous options: Sequoia and Kings Canyon National Parks (California): California is for climbers. And the parks of Sequoia and Kings Canyon usually have far fewer crowds than uberpopular Yosemite. Grand Teton National Park (Wyoming): Climbers come here from all over the world and enjoy a full range of challenges.

Ice climbing

Pictured Rocks National Lakeshore (Michigan) This is probably the most adventurous challenge of them all -- the specialty sport of ice climbing. And Pictured Rocks National Lakeshore in Michigan's remote Upper Peninsula is just the place to do it. Climbing season here typically runs from mid-December until early April. Two other adventurous options: Wrangell-St. Elias National Park & Preserve (Alaska): The nation's largest national park in area is also host to ice climbing. City of Rocks National Reserve (Idaho): Learn more about ice climbing at this reserve near the border with Utah.

People in wheelchairs

Everglades National Park (Florida) The National Park Service has designed wonderful areas for people who use wheelchairs and the people who come with them. One of the best for visitors with mobility challenges is Everglades National Park. Wheelchair-accessible trails here let visitors get up close to South Florida's wild denizens, including egrets, turtles and the big prize sighting -- alligators! Two other adventurous options: Congaree National Park (South Carolina): Venture deep but easily into an old-growth, swampy Southern wonderland on the wooden Boardwalk Trail. Great Sand Dunes National Park and Preserve (Colorado): Plow right into these dunes by signing out a special, sand-friendly wheelchair.