Here is a Google Earth image of Nine Mile Prairie.
I added a red border to show the area open to the public. The geometric area on the north side is a Post-World War II/Cold War era set of ammunition bunkers now owned by the Lincoln Airport Authority and used by various entities as long term storage facilities.
There are two state historical markers near the northeast gate:
And here is a view showing Nine Mile Prairie in relation to the city of Lincoln, Nebraska: