Above: the State Game Lodge at Custer State Park, built in the 1920s, with its two recent wings.
One way in which Custer State Park resembles a mini-Yellowstone is that it offers a few examples of "parkitecture," the building style of the 1900s-1920s that features massive timbers, rustic stonework, and an overall "hall of the mountain king" effect. (You can see more examples at the Parkitecture web site.)
Custer's Peter Norbeck Visitor Center (above) suggests the Norris Geyser Basin Museum in Yellowstone--classic parkitecture. Here (below) is a detail of the copper downspouts:
The visitor center at Wind Cave National Park (above), built by the Civilian Conservation Corps in the 1930s, offers a relaxed and inviting face as well.
Although I do not visit just to see the buildings, I make a point of experiencing them—having a drink in the bar while watching tourists interact with the buffalo, wandering the museums, eating a meal in the dining room. It's all part of slowing down and being there.