@Seapeekay Don't bother with Gran Via, it's basically like Oxford Street, unless you want to see the biggest Primark in Europe xD but in Calle San Miguel there's the oldest restaurant in the world, it has the Guiness World Record certificate n everything, kinda neat. Have fun!
@Seapeekay So many things but, for eating, check out el Mercado de San Miguel, La Campana in Plaza Mayor for the bocadillos de calamaris, or Taberna La Fragua, a really good bar de tapas close to Sol, which is the main plaza in Madrid that you shouldn't miss seeing either :)
@Seapeekay Sightseeing, see el Parque de Retiro, and the Palacio de Cristal, cool vintage shops and good bars around the barrios of Chueca and Malasaña, and for art the Prado is very cool