I have stayed twice in this 'slightly different' hotel. You don't stay every day in an old watertower. On the first occasion I stayed in a junior suite on the upper floors, the second time in one of the two floor-maisonettes. The rooms show great attention to detail, have a look at their website and you will know what I mean. The junior suite seems to be better value for money and offer greater views over the city. The service is outstanding and makes you feel genuinely welcome. Every(!) member of staff is extremely friendly and helpful. Make sure you try the breakfast and reserve yourself a table at the restaurant on the top floor for an evening you won't forget easily. You never know you might bump into Brad Pitt or Madonna, they both stayed here.
Long term parking is available directly under the hotel, but it is public and you will have to pay for it. However, it is not very pricy and can be added to you bill if you wish. The location is the only thing, which prevents the hotel from getting the top mark by me. You don't get the great views of the rhine or the old city, if you would choose to stay in one of the hotels on the river bank. But I would prefer anyday a stay in this hotel with character, which made both my trips to Cologne 'A stay with a difference'!