The historic centre of Cologne has various buildings and monuments to see — but by far the biggest, and the only one that it's essential to see, is the city's famous "Dom" (i.e. cathedral). Located smack bang in the middle of town — just outside the main train station — the Dom is so bloody enormous, it's quite impossible to miss. With its impressive towering exterior, and its gorgeous arches and windows inside, it's believed to be the largest fully-preserved gothic structure in all of Europe. Entrance is free, too: just wander in and look at your leisure. This morning, before I scooted out of town, I checked out the Dom, and got somewhat blown away by it. No, really: it was a super-windy morning; and while standing in the exposed plaza in front of the Dom, I literally got blown inside.