We drive by there every June on our way to Decorah IA to see the "Decorah eagles". There's a fairly large parking lot there, big enough for class Cs for sure maybe even a few fifth wheels. There's a museum there that has information there for you.
As mentioned earlier the mounds themselves are fairly easy to get to and are not very prominent, not exactly like going to Arches National Park to see the arches but still interesting. If you're going to be in the area stop and visit McGregor IA a neat place. Another neat place is in Prarie du Chien right across the river, Villa Louis. We enjoyed that too.
Dan