I stayed at BOTH Carlos V and Hotel Europa during my visit to Madrid in May 2000. There was'nt that much difference. Carlos V has better amenities, and the rooms were a bit alrger, but that $50 difference could be put to better use, IMHO. Europa had a nice staff , and the cafe next door made a mean tortilla de espana. Also, it overlooks Puerta del Sol, so an outside room could be a bit noisy.