Alfonso X is one block long running from Juan Bravo to Rafael Calvo. It's just a block to the Ruben Dario Metro stop. It is fairly upscale, but I lived a block from there for a month when I first got to Madrid in 2003. It is a residential area with several restaurants and bars nearby, but no real nightlife within walking distance. Cross over Castellana and you are in Barrio de Salamanca with lots of shopping and still no nightlife!