Karlštejn Castle is a large Gothic castle located about 30 km southwest of Prague above the village named Karlštejn.

The castle was founded in 1348. It was built by Czech King and Roman Emperor Charles IV as a place for safekeeping of the royal treasures, especially Charles's collection of holy relics and the coronation jewels of the Roman Empire. The first stay of Charles IV in the castle is documented in 1355 when he came to supervise the building works as well as the decoration of interiors, especially the castle chapels. The construction of the castle was finished in 1365 when the Chapel of the Holy Cross situated in the Great tower was consecrated.

At the outbreak of the Hussite wars the castle became the place for safekeeping of the Czech coronation jewels, which were kept here, with the exception of several short-time breaks, for nearly 200 years. The castle was reconstructed in late Gothic style after 1480 and in Renaissance style in the last quarter of the 16th century. The present appearance of the castle comes from the last reconstruction, which was carried out in the purist neo-Gothic style by architect Josef Mocker at the end of the 19th century.

Individual buildings of the castle are situated at different height levels expressing their importance. Dominating on the hilltop is the 60m high and separately fortified Great tower built upon massive walls (4-6 m of thickness) that houses the Chapel of the Holy Cross. From there one can step down to the Marian tower, the five-storied Imperial palace and come to the Well tower and Burgrave's palace located at the lowest level.

Entirely unique is the original decoration of wall paintings dating back to the 14th century, collection of 129 panel paintings by Master Theodoric in the Chapel of the Holy Cross (the world largest if its kind), the largest portrait gallery of Czech rulers in the country, exhibited replica of St. Wenceslas crown - the coronation crown of the Czech Kings as well as the unique castle well.

Karlštejn Castle is one of the most famous and most frequently visited castles in the Czech Republic.