Glaciers that moved across northeastern South Dakota roughly 20,000 years ago left behind a trove of glacial lakes, resulting in a haven for bird watchers and outdoor enthusiasts alike. The northern part of the region harbors over 120 glacial lakes and the renowned Glacial Lakes and Prairie Birding Trail, one of the most productive waterfowl breeding areas in North America and home to over 300 species of birds. In the southeastern part of South Dakota is Sioux Falls, the state's cultural epicenter and largest city. The 14-mile (23-km) Greenway Trail makes a sweeping loop around the city's impressive falls. In the summer, be sure to take in the annual Yankton Riverboat Days and Summer Arts Festival, which features over 150 arts and crafts booths, a parade, dance shows and children's activities. Watertown is the hometown of celebrated artist Terry Redlin, and visitors can see over 130 of his original paintings at the three-story Redlin Art Center.