Just off the Plaza Mayor, in the Plaza de la Puerta Cerrada, 7, you will find El Madroño a great little bar which serves fantastic tapas. The entrance to the bar is has tiles on the wall which depicts Velázquez’s painting Los Borrachos (the drunkards) - inside the bar you will find many such tiled paintings; one of the most interesting shows how the Madrid coat of arms has changed over the centuries and is located directly behind the bar. Drinks come with generous portions of tapas - I was offered a olives and patatas bravas (roasted potatoes with a chilli sauce) - and are served by friendly staff. The bar also offers vermouth on tap and has a good selection of wines. You may also want to try the local licor de madroño.
Address: Plaza de Puerta Cerrada, 7 (Map)
Metro: La Latina or Tirso de Molina