In northwest America, Olympic National Park offers fantastic hiking, climbing and wildlife viewing opportunities, such as elk and marmots. But along its coastline is another little-known joy: tide pooling. At low tide, many of the craggy rocks along the park's shores harbour small creatures and fascinating underwater worlds. It's a fantastic activity for the kids to learn about life under the sea. Go alone or on one of the ranger-led programs. Expect to see giant green anenomes, sea stars and rock crabs.

The concept of a homestay, where you live with a local family, might seem odd in a country like the US but one of America's little-known national parks is not actually in the USA at all. The National Park of American Samoa is on American Samoa, out in the sunny South Pacific Ocean. Here you can stay with a family in traditional home (a fale), dine with them and help with activities such as cutting and drying leaves for weaving mats. Discover more American islands that aren't in North America here.

It's time to channel your inner pirate and take yourself on a treasure hunt. In the wilds of Arizona's Petrified Forest National Park – a rocky, barren landscape where ancient trees have turned to solid rock – a specially-created geocaching trail makes for a fun day out. Find hidden containers (geocaches) using a GPS device such as your phone, sign the park's logbook inside and leave a message for the next adventurers, then uncover another one. The trail takes you through some of the finest landscapes and geological formations in the park, and can be found using the Geocaching app.

Hiking, cycling and kayaking are common activities in many national parks across America but only in the Everglades National Park and Big Cypress National Preserve in Florida do they come together to create a thrilling fitness challenge. The Tamiami Trail Triathalon starts with a 15-mile cycle ride along a loop road from the Shark Valley Visitor Center, then a three-mile hike on a loop trail from the Oasis Visitor Center. Finally, the water element of this triathalon is done in kayaks – the 3.5-mile route from the Gulf Coast Visitor Center will take you gliding along the serene waters of the Everglades.

In the Giant Forest of Sequoia & Kings Canyon National Park, California, the world's largest tree stands tall. Named General Sherman, after an American Civil War general, it has an immense trunk with a circumference of 36 feet at ground level and 25 feet at eye level. It stands at almost 275 feet tall – though it isn't the tallest in the world, that accolade goes to Hyperion in Redwood National Park – and its mass is a total of 2,105 tonnes. Follow the Big Trees Trail to find this beast among other impressive sequoias.

Geothermal activity beneath the surface of the earth is common across America but it's not every day you get to bathe in the warm waters of a hot spring inside a national park. For a special kind of spa break, head to Big Bend National Park in Texas and seek out the Hot Springs Historic District, where you can take a dip inside the foundations of a historic bath house (pictured), right on the shores of the Rio Grande. Read about more amazing hot springs around the world here.

Yosemite has always inspired creatives, from the likes of photographer Ansel Adams to painter Chris Jorgensen. Today, it's still inspiring artists and at the Happy Isles Art and Nature Center, there are daily classes from April through October, suitable for all ages from 12 years and up. The classes are run by volunteers and will take you out into the Yosemite wilderness to paint or draw whatever inspires you the most. The Ansel Adams Gallery also runs classes focused on photography. 

Most people visit national parks in summer when the weather's warm and dry, but head to Denali National Park in Alaska in winter and you'll be in for a treat. Cold weather activities like skiing and snowshoeing are common, and the best part is dog sledding (or mushing). Take the reins and learn to mush a team of energetic huskies with Denali Dogsled Expeditions. You can even do overnight tours and stay in cabins across the park.

If you're not a thrill-seeker and jumping on a sled isn't your bag, there's still good reason to go to Denali National Park. Each year, a new litter of puppies is born to take over from the older dogs that will eventually retire, so come at the right time and you might just meet some mushers-in-training. If you can't make it in time to see the pups, there's a webcam that goes live when the litter is born. Who knew America's national parks could be so cute?

Eagles, bison and bears are among the more well-known wildlife you can spot in America's national parks but did you know there are also wild horses? On Assateague Island National Seashore, around 150 feral horses (meaning they're descended from domesticated animals) roam free. You can observe them from a distance (and definitely don't feed them, it could seriously harm their health), and once a year watch them swim during the Chincoteague Wild Pony Swim.

Some people visit national parks to find gorgeous landscapes, intriguing history and exciting wildlife. But if you're looking for something more profound, book onto a Balanced Rock retreat. Their yoga programs involve plenty of trekking, meditating and stretching in the great alpine outdoors of Yosemite National Park, and are occasionally paired with creative activities like writing.

Formed 7,700 years ago, this awe-inspiring crater lake, in the aptly-named Crater Lake National Park, is the deepest in the USA. Surrounded by 2,000-foot-high cliffs, it's an exceptional place for hiking with spectacular views all around. You can camp nearby at Lost Creek Campground which has a trail leading to the rim of the enormous crater – perfect for a sunrise hike to catch the view.

Come winter, Yellowstone National Park closes to the masses. With the crowds of summer gone and most of the hotels and campgrounds closed, it's as if the park is left to hibernate during the cold snap. However, on special guided tours with snow transport, you can explore its stunning landscapes to see the forests and wildlife in an entirely different light. Wrap up warm and try snowshoeing or cross-country skiing on one of these Grand American Adventures tours. Find our guide to Yellowstone and northern Wyoming here.

Glacier Bay National Park and Preserve is stunning. The snow-capped mountains, glassy waters, spectacular glaciers... it's a true pristine wilderness. But beneath the waters of the Gulf of Alaska lives a magnificent beast – the humpback whale. They come into the bay for food and are most prolific in June through August so come on a summer cruise and you might just see one breaching. Up to 50 feet long, they come to the surface to expel a breath of air, which bursts out at around 300 miles per hour. 

Biscayne National Park has a Maritime Heritage Trail, an underwater route that follows six shipwrecks off the coast of Florida. Only accessible via boat, three of the wrecks are easily explored by snorkelling while another three are best for experienced scuba divers. The ships mostly ran aground or sank during the 1800s and range from wooden sailing boats to steel steam ships. Discover more of the world's most stunning shipwrecks here.

Watching the first light cast shadows across a landscape and illuminate the world has a spellbinding effect no matter where you are. But head to Cadillac Mountain in Acadia National Park, Maine, and you'll be one of the first people in America to see the sun that day. Thanks to the high vantage point – more than 1,500 feet high – and its placement on the east coast, it's one of the first places to see light every day. The view is well worth the early wake-up call. Find our top sunrise spot in every US state here.

If you're serious about art, be it painting, sketching, writing or music, and you want to get your creative juices flowing somewhere truly inspiring, check out the National Park Service's artist-in-residence programs. There are more than 50 across the country – the parks each have their own version – and you could find yourself staying within the boundaries of a protected park for up to four weeks. 

In Alaska, Kenai Fjords National Park is a pretty decent surf spot, with waves rolling into its fjords. It's not something many parks can offer. Ocean Swell Ventures runs boat-based surf trips, taking you out into the best waves with boards and all. It won't be balmy but it's definitely an adventure – and a new way of surfing. 

If an adrenaline fix is what you're after, whitewater rafting is for you. Eschew the hiking trails and viewing platforms at Arizona's Grand Canyon National Park for a river rapids adventure. From the water, you not only get a thrill but also appreciate the enormity of this huge canyon. Or, bump over rocks and down small waterfalls in Glacier National Park's Flathead River in Montana. It's one of the coldest rivers in the country but the gorgeous views of surrounding mountains are worth the risk of falling in.

California condors, which have the widest wingspan of any bird in North America (up to 10 feet), were declared officially extinct in 1987. However, a recovery program in Pinnacles National Park is ensuring these impressive beasts climb their way back from extinction and eventually thrive throughout the area. There are now 86 wild condors which can be seen circling in the skies in Pinnacles. You can help the conservation efforts by reporting sightings – any information on the whereabouts of the condors is useful to the team of trackers.

National parks aren't all about nature. In Florida's Dry Tortugas National Park, you'll find an enormous, historic military barracks. Fort Jefferson may have never seen any action at its high brick walls – it's said there are 16 million bricks making up this behemoth fort – but it was still home to 2,000 people during the 1860s. Living conditions within the fort were less than ideal, with disease rife throughout. You'll hear tales of the people who lived and died there on a guided tour. 

Read more: Amazing animal encounters in every state

Climbing trees just got serious. If the big kid in you is yet to be satisfied, head to Redwood National and State Parks with Pelorus, a specialist experiential travel operator. It'll team you up with researchers and send you on the climb of a lifetime as you're trained and harnessed up to scale the giant California sequoias and redwoods. Reaching up to 300 feet tall, this will put any of your childhood records to shame and no doubt provide exceptional views of the surrounding forest and beyond. 

Read more: The most impressive bridge in every state

Golf probably isn't the first sport you'd think to try in a US National Park. Hiking, mountain biking or even rock climbing might seem more common activities. But inside Yosemite National Park, the Wawona Golf Course is a stunning place to play a round or two. Its nine holes are set among gorgeous tall pines, with pristine lawns and beautiful views of the park. It's not uncommon to see coyotes on the course which come from the surrounding forests.

Read more: The most terrifying destination in every state