Ruins of Radece Castle are located on a steep slope northwest of the main city square.
The castle was first mentioned in 1336 when its ownership came into the hands of the Counts of Celje (Celjski grofje). Previous owners are believed to have been Lords of Radece (Radeski gospodje), one of the branches of the Lords of Svibno (Svibenski gospodje). The castle was then destroyed in 1442, just like Zebnik Castle, but was later rebuilt and came under the ownership of the noble Mosconi family, which finally abandoned it in 1618. The sketches made by the famous 17th century historian and polymath Janez Vajkard Valvasor, also a member of the British Royal Geographical Society, show the castle already in the state of decay.
The castle was composed of a rectangular core with at least two defence towers and a larger palace yard. The ruins are nowadays mainly overgrown and hardly recognizable – it is still possible to see the remains of the palace yard and follow the walled castle core; the southeastern round and southwestern square defence tower are partially restored.