Hi,
There are a couple of tunnels on highway 16, pointed straight at the monument. Very interesting place to stop.
Also after leaving the monument, turn to the right, and go about 1/4 mile to a tiny parking area, you can get a side shot of Washington.
I stayed at Custer State Park, and I think it was boondocking (My favorite, I have plenty of solar). There is a 33 mile wildlife drive there, where you take a country road and see what can be found.
Fred.