I had really high expectations for the Mystery Castle. I love Roadside America, off the beaten path things like this. It was wonderfully weird.
You can only go into the/through the Mystery Castle on a tour. If you get there after a tour has started, they will wait till the tour moves to the next room, and you join them there and jump out once you get back to the room you joined it. It keeps the pace moving and since keeps goes from piling up. It's not packed, but the tour groups turn into decent size.
Each area you go into has something new and different. The tour guides know their stuff and were great. Definitely a fun place to visit!