Castle Habsburg in Switzerland. This one is used mainly for banquests and private parties. You can do a short walk inside but there's not much to see. The outside is more interesting. It's out of the way to go only to see it so if you ever find yourself castle hunting, skip this one.
Castle Lenzburg. Go here instead. This one is interactive, has lots of rooms to explore, and much more fun!
Flags of Castle Lenzburg- Augusta Raurica - Roman ruins in Augst, Switzerland. This was a good stop. It's free to wander around the the ruins spread over a fairly large area. We didn't get to them all.