Who doesn’t want to zoom down a 500-foot (150-meter) pile of sand? Just under four hours from Denver, Great Sand Dunes National Park is like the world’s largest sandbox. Rent sandboards in nearby Alamosa or Blanca, and you and the kids will be slipping, sliding, and soaring down some of the country’s tallest sand dunes. Of course, the park is great fun to explore on foot, too.

Waterfalls, wildflowers, wooded hollows, and wetlands exist just 75 miles (120 kilometers) from Washington DC. Shenandoah National Park is one of the best national parks for children, as kids can scout for the forest’s creatures, wander across pioneer homesteads, climb up kid-friendly summits, and more. Running along the Blue Ridge Mountains, visitors can explore the park via Skyline Drive, a winding, scenic, 105-mile (168-kilometer) drag that runs the length of Shenandoah.

When Mount Mazama erupted 8,000 years ago, its blown-off top left a rocky bowl that collected water. Today, this bowl is known as Oregon’s Crater Lake, the deepest lake in the country. If you’re visiting in the warmer months, older kids will love trekking beyond the rim and down to the lakeshore, taking a boat ride to Wizard Island—you can swim at select spots, too. If you’re with younger kids, stick to the scenic drive on the rim, and hike the easy trails to waterfalls and volcanic pinnacles.

In western South Dakota, wild rock formations that look like frozen sand dunes rise out of the prairie, giving this place its name: Badlands National Park. If the kids want to walk on the moon or Mars, there’s nowhere better here on Earth to do so. Badlands Loop Road (SD 240) will take you just about everywhere you need to go, connecting you to a dozen overlooks and several short, kid-friendly hikes, like the Window and Door Trails.

Acadia National Park protects the highest rocky headlands along the Atlantic coastline. And there are so many things to do in Acadia National Park: Munch on popovers at Jordan Pond, hike The Bubbles Trail if you have older kids, or explore creatures hiding in Wonderland’s tide pools.

Send the kids back in time with a visit to Congaree National Park, the largest intact expanse of old-growth bottomland hardwood forest left in the southeastern US. Outdoor family activities in national parks don’t get much better than in Congaree. Explore along floating boardwalks—yep, these majestic bald cypress trees sit in water—keeping an eye out for river otters, woodpeckers, owls, and more. Consider staying overnight so you can camp amongst the trees and stargaze.

Though small, Pinnacles National Park is one of the neatest family vacation spots in the US. A mere 90 minutes from San Jose, California, you and the kids can climb into talus caves, hike across volcanic rocks, picnic at Bear Gulch Reservoir, scout out pinnacles and ridges, and more. If you’ve got a family of early risers, head out in the morning to the High Peaks region. There, you can test your luck at spotting the park’s most famous resident: the endangered California condor.

The kids will go nuts for the world's longest-known cave system. About 90 minutes from Nashville, Mammoth Cave is a whopping 426 miles (685 kilometers) long. You and the kids won’t be able to explore all of it, but with a cave tour, you’ll go underneath Kentucky, stepping into this dark, subterranean, stalactite-rich world. If there’s a certain tour you’re eyeing—some are longer and some are kid-friendlier than others—book your tickets in advance via the park website.

Great Smoky Mountains National Park is home to waterfalls, wild forests, and mountain views. It's one of the most popular national parks in the country—and even better, it’s free to enter, perfect for families on a budget. A self-guided driving tour makes navigating the park easy. You can explore from the popular Cades Cove, looking for black bears and pioneer homesteads, and hike up Clingman's Dome. When you’re finished exploring the park, there’s plenty more to do in nearby Gatlinburg.