Karlštejn is a market town in Beroun District in the Central Bohemian Region of the Czech Republic.

The highest point is the hill Velká hora at 423 m (1,388 ft) above sea level.

The built-up area in situated in a valley of the Berounka River and its tributary, the stream of Budňanský potok.

The entire municipal territory lies within the Bohemian Karst Protected Landscape Area.

In 1952, the modern market town of Karlštejn was created by merging Budňany and Poučník municipalities and named after the castle.