A UNESCO World Heritage site. It took over 630 years to complete this monumental cathedral. In 1880 the cathedral was finally consecrated. Cologne's Dom is the first sight you will notice when taking the main exit from the central station. (If you don't see it, you've taken the back exit.) If you are in good shape, take the 509 stairs to the top of the south tower. It takes about an hour, so wear comfortable shoes, but it's worth the hike. Touring the cathedral is forbidden during Mass.