The castle served as a place for safekeeping the Imperial Regalia as well as the Bohemian Crown Jewels, holy relics, and other royal treasures.

Karlštejn Castle is located about 16 kilometres (10 mi) southwest of Prague in the Beroun District of the Central Bohemian Region, above the market town of the same name.

It is likely that there was not a progressive and cunning architect, but a brilliant civil engineer who dexterously and with a necessary mathematical accuracy solved technically exigent problems that issued from the emperor's ideas and requests.

Construction was finished nearly twenty years later in 1365 when the "heart" of the treasury – the Chapel of the Holy Cross situated in the Great tower – was consecrated.

In 1422, during the siege of the castle, Hussite attackers used biological warfare when Prince Sigismund Korybut used catapults to throw dead (but not plague-infected) bodies and 2,000 carriage-loads of dung over the walls,[2] apparently managing to spread infection among the defenders.

During the Thirty Years' War in 1619, the coronation jewels and the archive were brought to Prague, and in 1620, the castle was turned over to Ferdinand II, Holy Roman Emperor.

The Burgrave House formed the Karlštejn settlement, it was fortified with a two meters wide rampart, the Well Tower stood slightly lower.

Miners were brought in from the mining town of Kutná Hora, however, water was not encountered even after the depth of the well was 70 metres (230 ft), well below the level of the nearby Berounka river.

Considering the significant strategic weakness incurred to the castle by the lack of an independent water source, the existence of the underground channel was a state secret known only to the Emperor himself, and the burgrave.