This is a off the beaten path way of spending a nice saturday or sunday morning visiting a nice popular Madrid's neighborhood

You can take metro line 5 or 2 till Ventas, and visit the bullring. Then either take the metro again (line 5) one stop till El Carmen or cross the M-30 by foot and walk till the Mercado de las Ventas (Ventas market), a traditional food market with lots of interesting shops, butcheries, vegetables and fruits, fish, etc. Interesting and cheap to buy some olives, cheese or jamon. The market is in Virgen de la Alegria 10, minutes away from El Carmen metro stop or some 5-10 minutes walk from Ventas bullring.

After that you can go to Plaza de Quintana, a bit up in Calle Alcala, or you can take the metro line 5 one more stop till Quintana. Alcala street is full of traditional shops and it's a big shopping district where a lot of madrilians go to do their day-today shopping. Lots of shoe shops for those interested. In Quintana square you will see people selling/exchanging "cromos" (collectionable transfers for kids, usually with popular cartoons or football players). You can get cromos for any football player you may be looking for at very reasonable prices (10/15 cents). In that very same square there is a bar serving the best Patatas bravas in the world, Docamar, After you sample some bravas and a beer you can take metro line 5 from Quintana back to the city center.