National Mississippi River Museum and Aquarium

The only Smithsonian-affiliated institution in Iowa, the National Mississippi River Museum and Aquarium is a 14-acre campus in Dubuque's Port district that tells the full, extraordinary story of the continent's greatest river — from prehistoric geology to the golden age of steamboats to the complex ecology of today. Live animals including river otters, alligators, and more than 100 native species inhabit tanks and habitats throughout; outdoor exhibits include historic vessels and a working boat yard. Genuinely world-class and worthy of a full day's exploration, this is Dubuque's single most-visited attraction — and it earns the distinction completely.