[This is part of my vanlife series. I've spent 7 months and 25kmiles on the road in 2 years, exploring and rock climbing around the US]
We did a whirlwind drive through tour of Badlands National Park in South Dakota on our way from Ten Sleep WY to the New River Gorge WV. The park is easily accessible from the single Badlands Loop Road--most of the overlooks are a short, paved walkway from parking areas. Most of the hikes are under 2mi, often paved, and top out at 10mi. If you're driving through, this is a great place to stop for a day or two.
The Badlands have eroded over 500,000 years to reveal sediment deposits from 75 million to 28 million years ago. Some views of the park are miles and miles of rolling exposed sediment, and others are huge prairies.
We stopped at many of the overlooks and did the 1.5mi Door Trail and 0.25mi interpretive Fossil Trail. I'd love to do the 10mi Castle / Medicine Loop trail. We passed hikers who said they rounded a corner into big horn sheep!
There's two developed campgrounds in the park, Cedar Pass and Sage Creek. In early fall mid-week, there wasn't any problem finding a site. Cedar Pass has flush toilets and water; Sage Creek is more primitive.
If you're driving through this part of the country as we did on our cross-country road trip, it's a great stop between the Wyoming/Idaho area and the Wisconsin/Chicago area. There's Mt. Rushmore and The Needles within 1.5hrs or so.