Perfectly acceptable for a short business stay (or a night in transit), the Wyndham Köln is in a great location across the plaza from the central train station, with plenty of shops and quick serve restaurants minutes away.
You're literally 5 minutes from the Dom Cathedral and all of the many restaurants and shops on the high streets nearby.
The hotel is - what's a nice way to say it - old. The website photos are a bit misleading as the room was nowhere near as nice. Based on my room, it needs a renovation. The wallpaper, worn carpeting and not enough lighting just all point to an owner that is maximizing profits.
The bathroom literally is incredibly small and we found it literally uncomfortable. The shower did get suitably warm and the room attendants kept the bathroom as clean as possible.
The bed and linens were fine and clean (although the mattress is very soft). I liked the sparkling water and gummy treats, too.
The breakfast which was "meh" was pricey - €20. We ended up going to some of the local bakeries each morning and spent less and got better food.
During any non-convention time-frame, it's an alright place to stay as it probably is reasonably priced. For a convention, which prompted my most recent trip. The prices are ridiculous (throughout the city) which points to supply and demand!
If you need a place to stay for a quick trip - this Wyndham is ok. Just be mindful that it's 3 stars because it's not in the condition to warrant more.