Described by UNESCO as 'a masterpiece of gothic architecture', the Kölner Dom was declared a world heritage site in 1996. The construction of the gothic cathedral took 632 years, and when it was finally completed in 1880, it was the world's tallest building. The Dom stands an imposing 157m high and you will need to be in good shape if you want to climb one of the towers, although the view from the top is definitely worth the effort. view all details