22. Biscayne National Park, Florida

Annual visitors: 469,253

Fun fact: Locals call Columbus Day long weekend, during which the area is a draw for boaters, “the most dangerous weekend of the year,” due to the high frequency of boating accidents.

This park encompasses Biscayne Bay off the southern shore of Miami, and protects a portion of the Florida reef, barrier coral reefs that are endangered. The islands, such as Elliot Key, are actually coral formations covered with a thin layer of topsoil. The bay is host to marine life like manatees, mollusks, and countless species of rainbow-hued fish. There is a campground, and kayaking, snorkeling, and scuba diving are all popular activities.