SO COOL. I know its mad touristy but it is definitely something locals should experience so they can take family and friends when they come to visit.
The Whaley House is actually a legit haunted house recorded by the US government--something like one of six in the US. It's seriously legit and you feel all kinds of vibes. It has been preserved as the Whaley's had the bedrooms and you can walk through the downstairs and upstairs halls. It was smaller than I had expected but not lacking in effect at all. Also, the courthouse has been kept as is. If you live in SD, you have to check it out. Don't forget to walk up the street to see the old cemetery either!
You buy your tickets next door at six dollars each, and take your receipt to the door as your ticket. The woman working in the shop is awesome and really nice. They also have a ton of stuff in the shop that are pretty rad, from literature on the historical aspects of the house as well as lore of the area. There is some pretty sick artwork, and gift shoppy items in there as well.
Check it out--it's just a rad piece of history with some good lore and a fun place to take the family, especially if you are in the Old Town area. There are also people dressed in period attire to answer your questions as you move about the house.