Badlands National Park is located in southwest South Dakota and is famous for its rich fossil beds and dramatic landscapes. It has lots of beautiful hiking trails, great views, and two different campgrounds for you to choose from if you do decide to spend the night there.
Wind Cave National Park is also in the southwestern region of South Dakota, so you could conceivably visit both parks in one trip! Wind Cave is known for its huge underground cave system, which you can view by taking a ranger-guided tour. There are also lots of hiking trails, wildlife, and camping options in Wind Cave, so you could easily spend the night there if you wanted!