Heiligenkreuz Abbey (Stift Heiligenkreuz, Closter Heiligen Creyz or Santa Crux) is a Cistercian monastery in the village of Heiligenkreuz in the southern part of the Vienna woods, c. 13 km north-west of Baden in Lower Austria. It has existed without interruption since its foundation in 1133 and is thus the second oldest continuously religiously functioning Cistercian monastery in the world.
Entrance to the abbey is through a large inner court in the centre of which stands a Baroque Holy Trinity Column, designed by Giovanni Giuliani and completed in 1739. The façade, as in most Cistercian churches, shows three simple windows as a symbol for the Trinity. Typically Cistercian, the church originally lacked a bell-tower, but one was added during the Baroque era on the north side of the church.
The abbey church of Heiligenkreuz combines two styles of architecture. The façade, naves and the transept (dedicated 1187) are Romanesque, while the choir (13th century) is Gothic. The austere nave is a rare, and famous, example of Romanesque architecture in Austria. The 13th century window paintings in the choir are some of the most beautiful remnants of medieval art.
The chapter house in the cloisters contains the graves of thirteen members of the House of Babenberg, including Duke Frederick the Quarrelsome, the last Babenberger. The remains of Blessed Otto of Freising are kept under the altar of the Blessed Sacrament at the east end of the presbytery.