The unique decagonal nave of this church opens to east into a choir which was completed about 1156. Much of the original furniture was destroyed in WWII and the structure required significant repairs. Yet the heavy, round-arch, romanesque design elements are evident.

The apse retains most of the original wall paintings, including the enthroned Christ, St. Gereon, and a bishop brandishing a sword. The windows are modern.

Opening off the south side of the decagon is a baptistry built 1242-45. By that time the gothic style had taken hold in German lands. The font itself is of a somewhat earlier date.

Opposite the font is a late gothic altar. The wall paintings date to the mid-13th century, about the time of construction.

One of the most striking features of the church is a chapel with a 19th century pieta. Although the gilded vault and variegated marble panels are eye-catching, the monochrome sculpture stands out even more.