The Osek Monastery was founded by a Czech nobleman called Milhošť who invited Cistercian monks from the Bavarian Waldsassen Abbey to his manor in Mašťov at the end of the 12th century.

The abbey suffered during a rebellion by the future Czech King Ottokar II, who sacked it due to its association with the Riesenburg family.

[2] The abbey's property came directly under the Prague Archbishopric, and the monastery was reestablished in 1626 with the support of Archbishop John Lohelius.

[2] During World War II, part of the monastery was forcibly requisitioned and sold to the occupying German army.

After the war, Abbot Eberhard Harzer and numerous monks faced investigations and false accusations of collaborating with the Nazis.

In 1991, the newly elected Abbot Bernhard Thebes moved to the monastery with a small community of monks.

[4] The monastery occupies a significant portion of the town's centre, with its most prominent feature being the Church of the Assumption of the Virgin Mary.

This three-nave basilica of Romanesque origin has a three-axis façade but lacks a large tower in adherence to Cistercian traditions.