Karlstejn Castle is a Gothic fortress commissioned by Charles IV, King of Bohemia, begun in 1348. It has served as a royal castle and vault for the Imperial Regalia, crown jewels and numerous holy relics. Matthias of Arras may have been the architect, but the structure is more notable for it's engineering achievements than it's design.
The elaborate multi-level fortifications and imposing towers are enormous, but fires and wars took their toll and the castle was reconstructed several times. The basic surviving structure is largely Renaissance in design, except for the wooden galleries which are in the French style and were added when the castle was restored in the last century.
The addition of these non-native details is typical of many European castles and palaces as they were restored over the last 150 years, (often by wealthy individuals). In this case, the addition of French details to a Czech castle prevented the monument from becoming a UNESCO site.