The door for the room uses a traditional key mechanism and requires turning the key to turn the latch. You cannot turn the knob. Therefore, when you pull the door shut, you have to pull it hard to engage the latch. This makes a loud bang, which can be heard at night if a neighbor comes/goes, e.g. toilet. Some thoughtful neighbors will use the key to rotate the latch before pulling the door shut. The beds are fine, but the mattresses are bit on the hard side. Some shampoo is provided (in packet), buy you may want to bring your own. There is no elevator, so you will need to carry your suitcase up some stairs (mine was up 3 flights of stairs). None of this was a big deal for me though, but you should know this before booking.
I had a single (one twin size bed) with a shower and small sink (shared toilet in the hallway). The room and hotel are impeccably clean. The location is perfect, next to the train station (3 blocks and 5 minute walk), old town (past the train station), and one block from the river walkway. There is a top-notch continental breakfast (rolls, jams, bread, cereals, fresh fruit, cheeses, meats, yogurt, juice (not fresh), coffee, and tea). Do not expect a hot breakfast though, which was fine with me. You get a soft boiled egg too. The front desk and housekeeping staff are so friendly and welcoming, willing to answer tourist questions or hold a conversation. Front desk staff all have good English. I have no complaints for the value. It is a perfect hotel for an unbelievably reasonable price if you are a solo traveler looking for a bed to sleep on while visiting Koln for sightseeing. There is a hair dryer in the room, a closet, small desk/chair, and a small flat screen TV with many german channels, 1 french channel, 1 italian channel, and 2 english channels (CNN and BBC). Maybe more, but that is what I noticed. S13 tram takes you straight to Koln airport from train station in 15 minutes. Leaves at least twice hourly for 2.80 euros.
Highly recommend. (Don't expect the Marriott though, which is one block away and 3-4x the price).