Not that far from David are the famous Falls of Sioux Falls and the Big Sioux River. Niagara Falls they're not but they're interesting and a spectacular place to wander around.
There's a duck on that little island. We watched a duck seemingly fighting the current and desperately struggling out of the water. Then another one. Obviously they do it for the tourists. They know which side their bread's buttered.
We kep hearing ghostly train whistles. This looks like a working railway but there's nothing to stop you walking on it.
Meanwhile people were happily clambering all over the rocks, which are a pretty pink colour.
This is what it looked like. The stone is Sioux Quartzite, quarried on site. The building was state-of-the-art at the time.