Day 4 Our journey advanced today as we crossed the Missouri River. We left behind what was simply beautiful farmland and have entered what I'm now calling the "wow" phase of our trip. Just before crossing the Missouri, however, we stopped off at the South Dakota Hall of Fame. I think one of the pleasures of South Dakota is that you can see all of the main attractions without having to leave I-90. South Dakotans flock to I-90 like bugs to light; at least, when it comes to setting up a tourist attraction. There are more billboards in South Dakota than anywhere else I've ever been, and most of them are for Wall Drug. More on that in a bit.