The important medieval land trade route from Freistadt to České Budějovice was often threatened by traps and robbers. Several guard castles were probably built to protect it, such as Louzek, Sokolčí, Pořešín and Velešín.

Louzek used to consist of three parts. The small core of the castle itself consisted of a tower as well as residential and other buildings in the corner, which was protected on the west and north side by a moat, ¬while a moat was cut into the rock in the west. The rock cliff in front of the castle core was fortified and protected the access road. On the northeast corner of the rock formation was a high fortification. A moat and rampart surrounded the entire complex. A relatively small bailey was attached to the steep slope above the Malše in the south, while a wall and moat were in the west and north.

Unfortunately, written reports about the castle are rare.

In 1421 the castle was first mentioned in written sources with the castle lord Petr Harrachéř of Louzek, at that time the Rožmberk burgrave of Vítkův Hrádek Castle, and the fortress first appears in written documents. A later report from about 1440 mentions that the castle became the property of the Malovec family of Malovice. On 1 August 1448, the brothers Jan, Diviš and Bohuslav of Malovice wrote the castle over to Oldřich II of Rožmberk, thus making it part of the Nové Hrady estate. It was subsequently quickly let go, because only 12 years later, Oldřich of Rožmberk sold the estate to a certain Bárta and his son Kříž. In 1541 the castle was mentioned as a ruin.