My brother Ben is here to visit: thanks to him, I now know that just half an hour by bus out of Madrid you come to Hoyo de Manzanares, a village in the Sierra de Guadarrama from which you can get soonish out into nature. This photo is of an imperial eagle, but you might have to take that on trust. There was a great deal of good graffiti on the way back.
For those of you with a little Spanish (and a lot of time on your hands), there's a review here of Marian's and my translation of Boris Savinkov's Конь Бледный.