Not much survives of old Cologne anymore. The city, which had (and still has) a heavy industrial base was almost completely flattened during Allied bombing runs in the Second World War. But its remarkable Cathedral survived, and so did this group of narrow medieval homes and storefronts just off the banks of the Rhine River. I was surprised by how narrow these buildings were and am under the impression that taxes at that time were proportional to how wide your business frontage was, so the tendency was to build them narrow and tall (owners lived above their shops).
The city is now a lovely destination, slightly off the main tourist track, with interesting sights including its magnificent cathedral (itself a UNESCO World Heritage Site) and many ancient artifacts dating back to the days of Roman occupation.