No visit to Cologne is complete without a visit to Cologne Cathedral. Located in the center of this city, the fourth largest in Germany, the Cathedral dominates the skyline. Started in the year 1248, it was completed a mere 600 years later. It is a massive edifice, larger than Notre Dame, and of a simile architecture. The most stunning part of the Cathedral is the stain glass windows. I assumed they were modern glass, but it turns out they aren’t. They survived world war 2, because they were removed by church officials, prior to the start of the war. In terms of your visit, it is still an active church, so admission is free and open to all.