The Sheyenne Grasslands are the closest thing to a national park near Fargo. Don't let "grassland" throw you. This is rolling prairie laden with plenty of things other than grasses.
Imagine you are like a cowboy in the Old West or a pioneer seeking a place to settle. The Sheyenne evokes that kind of feeling. Occasionally these pastures may be inhabited by livestock, but there is plenty of space for both man and beast. A segment of the North Country Trail runs through the reserve and is the best-marked trail.
Camping is allowed and there are plenty of shady groves that would be ideal for an overnight stay. The groves are also good for backpacking in. Horseback riders and bird-watchers use the park too. Make sure you have pants there, as there are tons of grassy things that might not like your skin--I went in shorts and had a horrible rash for 2+ weeks. Nonetheless, the place has fantastic hiking and few visitors.
Finding a suitable entry point can be a problem as the Sheyenne is not clearly marked. One entry point I found was a wildlife viewing area aboout two miles from 18 on 27. Look for the brown sign with binoculars. There is a ranger station in Lisbon on the western edge (on 27) for seeking more information