Puna, have you considered suggestions about Madrid surrounding areas?? It seems the city center has been fully discovered here but if someone comes to Madrid for more than 5-6 days, I would also suggest little excursions to some towns around where you can go by train (cercanías) and will take you 30-45 mins. Pretty cool to visit and find cultural wonders, i.e., Alcalá de Henares, Aranjuez, etc. Or maybe this could be opened as a new topic!