It was a sixteen hour drive to Mt Rushmore. We took two days to drive it so that we could have a break halfway along the ride. Sixteen hours in a car packed to the ceiling with camping gear and people can wear on your nerves a bit.
And South Dakota is a whole, flat, lot of nothing.
For a long, long way.
If you see anything even remotely interesting (like a human skeleton walking a dinosaur skeleton on a leash) you'd better stop. And I'm not kidding.
The sight of something other than flat land and no buildings means "there is a bathroom and food here, maybe gas, and who knows when you'll see any of that again".
I don't know the number of times we would get hungry and decide to stop for lunch and not be able to find anything, anything, to eat. We would make a statement along the lines of, "Let's pull off at the next exit and get some lunch, not fast food though, maybe a Cracker Barrel!" Then as the next exit would come into sight, we would see nothing. No signs advertising gas, lodging or food. No buildings. Just a road heading off into the distance and disappearing.
We nearly starved.
We ate gas station food to survive.
The isolation was terrible!
We learned early on to get gas when we saw it even if we weren't low.
Finally, after hours and hours and hours, we started to see hills and itty bitty mountains.
Mt Rushmore was just over the horizon.