Margrave Leopold III founded this abbey. It was built in the 12th century and subsequently gained an overlay of Gothic and baroque additions, with some 13th- and 14th-century stained glass still in place. The Romanesque and Gothic cloisters, with some 300 pillars of red marble, date from 1240. Some of the dukes of Babenberg were buried in the chapter house, including Duke Friedrich II, the last of his line. Heiligenkreuz has more relics of the Holy Cross than any other site in Europe except Rome.
Today a vital community of 50 Cistercian monks lives in Heiligenkreuz. In summer, at noon and 6pm daily, visitors can attend the solemn choir prayers.