Kost was originally built after 1371, probably by Benes of Wartenberg, who had the long hall and tower erected as a defensive stronghold. It was then acquired, in 1456 by John Hasenberg, but he took part in a rebellion against his king ,George of Podebrad and his son sold Kost and Trosky to John of Schellenberg, in 1490. After 50 years, Jan of Biberstein had the “Renaissance” wing built, with the big kitchen. His niece inherited Kost, and her husband, Krisof Popel of Lobkowitz, added the brewery, the “Lobkowitz” palace and other farm buildings, which were fortified and joined to the castle. Albrecht of Waldstein’s plans to redesign Kost into a country home while remaining a stronghold were halted by his death in 1634. In 1635, a part of the Castle was destroyed by fire after which it ceased to be inhabited by the proprietors. Bought by the Czernins of Chudenicz, the castle apartments were used as granaries at end of the 17th century. The Castle suffered during the 30-years-war and was to be destroyed .
After 1867 it was in part reconverted in neo-gothic style. In 1798 Casimir Netolitzky bought Kost and the surrounding lands and entailed the property,ensuring inheritance by male primogeniture . Kost later passed by marriage to the dal Borgo family (1889) and then to the Kinsky family (1993).
The Castle is dominated by the angular White Tower, five storeys high, the south-eastern part pointing towards the Plakánek valley. The tower is a part of the battlements erected from stone blocks. It was destined to the defence. The mansarde roof dates only from the 18th century. The Castle has a smaller cylindrical tower from the end of the 14th century close to the main gate.