Near the spring of Krupa, roughly 4 km from Semič once stood one of the largest castles in Bela krajina, castle Krupa. The mighty building had stick walls that were additionally reinforced with 5 towers in Valvasor times. It was built in the 13th century. Castle Krupa had 4 corner towers and a multi-story arcade courtyard. In the 19th century, it was the administrative center of Bela krajina. In 1942 the partisans burnt it down to prevent the occupying forces from taking it. Only the granary remains.

The first owners of the castle were supposedly the noble family of Babonić from Croatia. The castle was first mentioned in 1352 as “von der Crup”. In 1427 the castle was mentioned as “castrum Cruppa”. The Babonić family were relatives of Count Ursini-Blagaj. Counts Ortenbužani gained the castle and land by marriage in the middle of the 14th century. After the counts died out in 1418 the castle went to the counts of Celje and remained in their ownership until 1456. The castle was then transferred to the Habsburg family.