Last weekend I went to Madrid

with R. We stayed there from Wednesday night to Sunday morning. We had a nice hotel at Calle Campomanes just off Plaza de Isabel II where you have the Opera metro station. It takes just 30 minutes on the metro from Barajas or Aeropuerto on line 8. Then you have to change to line 10 at Nuevos Ministerios and again to the R-line at Príncipe Pío, and it costs just 1 euro.
My reasons for going were two. I wanted to hear the Spanish language about me, and I wanted to visit the Prado to see the Spanish Golden Age painters, from Murillo and Velazquez to Goya. We stayed at the Prado for nearly a whole day, just visiting the first floor where you have the paintings from 1550 to 1850. I could have gone the next day as well. It was great.
From Campomanes you walk down to the Prado in twenty minutes. Down the Arenal, crossing Puerta del Sol, to the right down Carrera de San Jerónimo to Plaza Canovas del Castillo. Then you are nearly at the entrance where you pay 6 euro to get in.