I tell Rosa, the concierge of this block of flats, that I have forgotten my key. "I can't do anything, " she tells me, "I don't know you." She speaks with such a thick Hispanic accent that I can scarcely understand her. I mention some names and gradually win her trust. She allows me to try out a skeleton key on a lock she keeps at the desk. It works. A metal latch detaches itself from the mechanism giving me access to the flat.