Constantin's place is exactly as described: very stylish, well located (VERY close to the Rathaus and walking distance to all places in the Alststadt Wien (and beyond if you're adventurous)). The beds are very comfortable and the place is quiet, so we had no trouble sleeping. The place was also very clean and taken care of. Although we didn't meet personally, he and his team answered our questions promptly, + they all seem very nice people. Highly recommended!