The Dells are a natural lake/river/hills/rock formation in north central Wisconsin that are beautiful. Like a mini, forested Grand Canyon. They are beautiful. You can go through them in a boat or climbing on some of them. In the town "Wisconsin Dells" there is alot of touristy shops and theme parks, and water parks. It's a pretty big tourist industry.
http://www.wisdells.com/home.cfm