Seriously, it is amazing amazing. Built at the height of Gothic gorgeousness by people without machines, electricity, computers, with an expected life-span of 40 (as long as the plague didn't get them). We also took the fast train from Frankfurt and we were going 250 km/hour - which we know because the entire train was a computer and the train told us.
Cologne itself was fairly well bombed in the war (except for the churches) so that city itself was a mismash of the old and the new. We did totally enjoy sitting in the main plaza and watching Germany play Italy in the European cup. (though the Germans were not very happy with Super Mario...)
(The Dom is also in the 2008 Where the Hell is Matt? video (around 3:30), which makes me really happy)