Groß St Martin is a lovely church from the 1200s. While it is much more basic than the cathedral,…read moreit is still quite nice and is well worth stopping by as you walk through the old town. The church itself is pretty, but the really impressive part is the excavation Roman ruins in the basement. They aren't huge, but it is a unique experience, and they are well signed and maintained. The church is free, but there is a ,50-cent fee to walk down into the excavation (they have laminated descriptions in four languages, but the signs are in German). Definitely worth the ,50 cents to see the ruins!

Okay, while I didn't go inside (and I'm not even sure if you can go inside - I didn't check) this…read moreis still a pretty awesome place to check out. Like the towers of the cathedral and Martin Luther's church, the tower of the Historic Rathaus can be seen from most parts of the city, however the impressive nature of the building only comes to the for when you actually get up close to it. Basically the tower is covered in statues of various celebrities of the city. I have to be honest that I don't know who precisely the statues represent, but apparently one of them is a witch. However, even though I don't know the identity of the statues, it is still pretty cool to spend some time admiring the architecture.

If you're the sort of tourist who likes to learn a little about the social history of the places…read moreyou visit, and if you speak German, then I recommend popping into the City Hall. There are a couple tapestries and paintings to view that will give you insights into the city's history, and often art exhibits and such that will give you a sense of the current state of affairs in Cologne. There is also an atrium explaining the legend of the mayor and the lion. However, you need to speak/read German, as virtually nothing is written in English.