West of town (1.5km), this extensive open-air museum includes 18th- and 19th-century buildings, a folk history exhibit featuring the creepy Devil's Finger (a finger cast in pewter with various spooky legends attached to it), and the ruins of the castle. But the centrepiece is Hamar's tumbledown medieval cathedral, now protected inside a stunning glass enclosure.
The grounds themselves are free to visit and open all the time, and you can also peer through the glasshouse-like structure that surrounds the ruined cathedral, but to get inside this or any of the other museum exhibit buildings you'll need a ticket.
It's a pleasant walk or cycle from town along the lake shore to the museum.