Cologne Cathedral, Germany. Construction began in 1248, was halted around 1560,  restarted in 1814 and was completed to its original medieval plan in 1880. The builders in the 14th century created a pastel light effect that remained unique among medieval churches. It is preserved in the cathedral choir to this day. The oldest window dates back to the 13th century, the most recent window was created in 2007 by Gerhard Richter. Source

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