St. Gereon’s Catholic Church is a lovely example of an historic religious building in Cologne. The site of the church is considered sacred, second only to that of the famous Dom. The use of the site for a church building dates from the 4th century. The currently building is noted for its interesting architectural features, and its beautiful stained glass windows. Inside it has a long choir area built on to a ten-sided domed structure dating to Roman times. The building’s main roof is the largest of its time period.