The ruined castle Nyköpingshus hosted some violent times in the Swedish monarchy. The bickering among King Birger and his two brothers, Erik and Valdemar, peaked in 1317 when Birger invited them to a ‘peace banquet’. When they arrived, he hurled them into the dungeon and threw the keys in the river, letting them starve to death. It didn’t do Birger much good, as he was driven to exile in Denmark the following year. You can wander around the ruins any time.
This cheerful episode is recreated each summer as The Nyköping Banquet, a traditional play; ask for a schedule at Sörmlands Museum.