Karlštejn Castle is a Gothic fortress located about 30 km southwest of Prague, Czech Republic. The castle was founded in 1348 by the Czech King and Holy Roman Emperor Charles IV as a place to store the royal treasures, including the imperial coronation jewels.

The castle consists of two parts, the lower castle and the upper castle. The lower castle, with its residential and administrative buildings, served as a seat of the king and his court. The upper castle, a three-story building with a cylindrical tower, was used to store the royal treasures.

The castle is also famous for its Chapel of the Holy Cross, which is decorated with frescoes and gold leaf. The chapel is a masterpiece of Gothic art and was used for the coronation of the Czech kings.

Today, Karlštejn Castle is one of the most popular tourist attractions in the Czech Republic. Visitors can take a tour of the castle and see the royal chambers, the treasure vaults, and the chapel. The castle also hosts cultural events, such as concerts, exhibitions, and historical reenactments.