Headed east after Sturgis there's a nearby museum with over 275 classic cars, 60 tractors, 60 motorcycles, and tons of antiques and memorabilia. The Pioneer Auto Museum is 160 miles east of Sturgis, just off I-90 in Murdo, SD. http://www.pioneerautoshow.com/
Mitchell, South Dakota, 75 miles east of Sioux Falls on I-90, is home to the Mitchell Corn Palace, an impressive structure covered with corn and other grains. I had lunch with Bill & Cheryl, riders from southern Wisconsin, who visited on a trip to Mt. Rushmore. There's even a Corn Palace Festival.