Take US 16A south from Mount Rushmore for the challenge of Iron Mountain Road. This road through the Black Hills is only 17 miles long, but it contains 314 curves, 14 switchbacks, three pigtails (where the road loops back over itself), and three tunnels blasted through the rocks, as well as a glimpse back at Mount Rushmore through the trees. You'll want your wits about you for this one, as it's a slow, tight, technical ride through the hills. It might not be a bad idea to practice low-speed maneuvers in a parking lot before tackling this one. You're going to need them.