My family toured Mt. Rushmore in probably three hours, but I guess it depends on how much you like to hike. We also spent some time at the nearby Crazy Horse monument, which is definitely worth visiting (and huge in comparison to Mount Rushmore. All of Mt. Rushmore can fit in the face of Crazy Horse). Also, our favorite stop in that area was Custer State Park. Lots of bison herds and wild burros (donkeys) roaming the park. Beware of the donkeys--they will stick their heads in your car windows and try to lick you/steal your food. When we went, our halfway point was Sioux Falls, SD.