Hola! I was in Madrid for one day back in November (stopping in between Barcelona and Lisbon). I managed to see both the Prado and Reina Sofia Museums, which I would consider must-see attractions whenever one is in Madrid. If I recall correctly, I first took took the metro to the area around Plaza Mayor and walked towards El Prado from there. Reina Sofia is fairly close, so that makes it pretty easy for you! After that, I went towards the Palacio Real and found a great place to get some churros con chocolate. All in all, a pretty good ten hours or so!