Well, I'm studying in the town of Aachen and so I'm used to see the beautiful cathedral hidden behind large papers as they are rebuilding it. Of course this cathedral can't be compared to the one in Cologne, but it's definately worth a visit, also maybe in combination with the treasure chambery and of course a guided tour through the cathedral (especially if the cathedral is still hidden). You definately shall try the "Aachener Printen", some kind of gingerbread with chocolate.