17. Kenai Fjords National Park, Alaska

Annual visitors: 321,596

Fun fact: Enormous glaciers grind the bedrock into a substance known as rock flour, which appears as a milky substance in the waters around the park. 

Alaska has eight national parks, each of them worth visiting for the beauty of their incredibly, untouched wilderness. Kenai, being close to Anchorage, is one of the more accessible, and many cruise lines use its headquarters in Seward as a launch point. The geography here is stark, with massive glaciers, fjords, ice fields, and mountains. Despite the rough terrain and cold temperatures, lots of animals thrive here, sea lions, orca whales, otters, and adorable puffins among them.