(ARA) - Each year, hundreds of millions of people visit the 397 destinations that comprise the country's National Park System. Summer is the ideal time to explore many of these parks, as the kids are out of school and activities in the parks are in full swing. Here are four national parks that are worth putting on your family's life list. Yellowstone National Park Spanning parts of Wyoming, Montana, and Idaho, Yellowstone National Park tops the list. Yellowstone was the first national park, created on March 1, 1872, in an act signed by then President Ulysses S. Grant, and it is the eighth-largest national park in the United States, which means there is a lot to see and do. It is home to the most geologically active lands on the planet. The gushing geysers and bubbling hot springs are the park's signature features. But the wildlife is famous, too. Get ready for the priceless look on your children's faces when they first see a bison crossing the road. With all this action, it is no wonder that Yellowstone is one of the country's most-visited parks as well. "If you want to miss the crowds, enter the park early in the morning, which is a great time to see the wildlife, too," says Nathan Borchelt, an editor and national park aficionado at GORP.com. "Or better yet, stay the night in the park for sunset views that day-trippers rarely see." Great Smoky Mountains National Park Covering more than a half a million acres, Great Smoky Mountains National Park in North Carolina and Tennessee is the most-visited national park in the country (drawing in around 10 million visitors annually). This park makes the list because it provides easy access to nature and is within a day's drive of nearly a third of the U.S. population. The park has nearly 800 miles of hiking trails and 16 mountain peaks higher than 6,000 feet. Families will see plenty of diverse wildlife, such as black bears, elk and a diverse collection of fauna and flora. Also, the park encompasses more than 90 historic buildings to explore. Acadia National Park Acadia National Park near Bar Harbor, Maine, delivers the full outdoor experience. It was the first national park created east of the Mississippi, and it is best known for its boulder-lined coast and former carriage-path trails that wind through the forest. Go hiking or trail running on Cadillac Mountain and enjoy the beautiful views and fresh mountain air. Also, explore the shores and islands with the family by kayak or canoe; areas such as Eagle Lake and Porcupine Island are stunning. Be sure to snag some of the area's famous lobsters and blueberries. And if you have time, plan a day-trip to Nova Scotia on the ferry. Grand Canyon National Park Grand Canyon National Park, also jokingly known as the eighth wonder of the world, brings in more than 5 million visitors each year. Hiking below the canyon rim or rafting a section of the Colorado River will ensure the whole family experiences more than just a panoramic view from the top (though that's one stunning view). Tell the children that the rock they just touched is more than 2 billion years old, and you will most certainly see a look of wonder. If you are really adventurous, you can plan a mule-trek into (and out of) the canyon, but be sure to drink lots of water and put on sunscreen, as it will get hot as you ascend almost 4,500 vertical feet. Top national parks for families