The earliest documented mention is of the Stiftskirche St. Cyriac, situated on a small hill, surrounded by the so-called "pond". It was built on the territory of a Frankish Königshof. In several excavation campaigns not only the so-called inner wall, mentioned in the document of 952, but also remains of the original monastery buildings were found.
An archaeological sensation was the excavation of a Frankish pottery kiln from the time around 600 A.D. The church belonged to the noble ladies' monastery founded in 946. It is a cruciform hall church with two eastern towers and a soaring western tower with a tower chapel. Romanesque building fabric from the 10th, 12th and 13th centuries. The building history can be seen partly from the outside, also from the inside. Several changes to the nave and transepts. Excellent sculptural work on the peculiar capitals. The bulwarks are interrupted in the nave by angel figures (Plantagenet style). In the northern transept now angular apse, in the southern transept round apse. High choir, probably an old crypt underneath (in earlier literature one is assumed).
Magnificent main altar and side altars (marble, alabaster) by Papen/Giershagen 1727/31. In the tower hall below baptistery and "hl. Grave". Above, organ loft with organ prospect from 1712. In the vault in front of the organ loft, paintings from the time around 1500.
Of the rich furnishings to mention: sacrament box of the 16th century, Pieta from the 1st half of the 15th century, so-called "Maria Schuß", venerated as a miraculous image, sculptures, including St. Cyriakus, according to a Geseke legend represented as a knight. In the northern transept wall reliefs with saints and martyr scenes. Adjacent to the southern transept is the former chapter house (now sacristy). Attached to it, remains of the Romanesque cloister. In the inner courtyard there are epitaphs of collegiate ladies.
The entire collegiate churchyard is surrounded by a beautiful quarry stone wall.