13. Kobuk Valley National Park, Alaska
Kobuk Valley is one of the least visited parks in the U.S., but it offers a landscape like no other. This remote Alaskan park is famous for its massive sand dunes, which seem totally unexpected in the Arctic. The Great Kobuk Sand Dunes stretch across 25 square miles and create a surreal scene against the surrounding tundra. Every year, hundreds of thousands of caribou migrate through the park, making it an incredible spot for wildlife observation. There are no roads leading into the park, so access is only by bush plane. That means solitude is practically guaranteed. Hiking and camping here are for the adventurous, but the rewards are unmatched. As with other Alaska parks, there is no fee to get in, making it one of the most unique free parks in the country.