The first time I visited Madrid was in 2003 and I stayed in the apartment of friend of my wife. The apartment was on Calle De Moratin fairly close to area where the Prado museum is located.
The 3rd floor apartment was on the inside of the building overlooking a narrow courtyard which many other pisos also looked into.
Every few days, we would do our laundry and part of the ritual was to hang the laundry outside on clothes lines suspended between two short metal poles attached to the wall.