St. Nikolaus (Cologne-Dünnwald)

The original structure was a short, three-aisled pier basilica without transepts and a flat ceiling. By the mid-12th century, three additional western bays, a nuns' gallery, and a tower were added. Investigations by the Rhineland Regional Association (LVR) in 2005 confirmed the church was built in a single continuous phase — and also revealed a second, southern tower demolished in the late 16th century due to structural deterioration. Until then the church had a twin-tower façade; today only the north tower remains.

When the south tower was removed, the nave roof pitch was raised from 42 to 54 degrees, and three small Romanesque windows in the west façade gave way to the large round-arch window with tracery seen today. The north aisle was vaulted in the 14th century and Baroquized in 1653, receiving cross-gabled roofs and a curved cap on its apse. After secularization in 1803, St. Nikolaus became a parish church; in 1875, the south aisle was rebuilt in a Romanesque revival style.

The altar and baptismal font were crafted around 1955 by sculptor Eduard Schmitz — influenced by Ernst Barlach — from Lahn marble. The altar houses relics of Saints Ursula and Gereon and bears the symbols of the four Evangelists: ox, lion, man, and eagle. The baptismal font is shaped as a stylized fish.

During renovations between 1997 and 2007, foundation remains were uncovered beneath the floor of the north aisle, running under the north wall toward an inner courtyard. These may be the remains of an agricultural building predating the church — if so, they would be the oldest evidence of human settlement in Dünnwald. An information panel inside the church documents the find.