The earliest documentary mention is of the Stiftskirche St. Cyriakus, situated on a small hill surrounded by the so-called "pond". It was built on the site of a Frankish Königshof. In several excavation campaigns, not only the so-called inner wall, mentioned in the document of 952, but also the remains of the original collegiate buildings were found.
One archaeological sensation was the excavation of a Frankish pottery kiln from around 600 A.D. The church belonged to the aristocratic convent founded in 946. It is a cruciform hall church with two east towers and a soaring west tower with a tower chapel. Romanesque building fabric from the 10th, 12th and 13th centuries. The history of the building can be seen partly from the outside and also from the inside. Several changes to the nave and transepts. Outstanding sculptural work on the peculiar capital zones. The bulwark ribs in the nave are interrupted by angel figures (Plantagenet style). The northern transept now has a square apse, the southern transept a round apse. High choir, probably an old crypt underneath (earlier literature suggests one).
Magnificent main altar and side altars (marble, alabaster) by Papen/Giershagen 1727/31. In the tower hall below, baptistery and "hl. Tomb". Above it, organ platform with organ prospectus from 1712. In the vault in front of the organ platform, paintings from around 1500.
Worth mentioning among the rich furnishings: 16th century sacrament house, Pieta from the first half of the 15th century, so-called "Maria Schuß", venerated as an image of grace, sculptures, including St. Cyriacus, depicted as a knight according to a Geseke legend. In the northern transept, wall reliefs with saints and scenes of martyrdom. The former chapter house (now sacristy) adjoins the southern transept. Attached to it are the remains of the Romanesque cloister. Epitaphs of nuns in the inner courtyard.
The entire abbey churchyard is surrounded by a beautiful quarry stone wall.
