I recommend the Queen Sofia Arts Center to all lovers of contemporary painting. It's not crowded, but you'll find works by Dalí, Picasso, and even Kandinsky! There's an amazing terrace with a stunning panorama and very stylish glass elevators.
Plaza Mayor is the central square and the busiest place in Madrid, where three streets converge – Calle de Atocha, Calle Mayor, and Calle de Toledo. The square has been awarded various epithets – popular, noble, majestic, austere, royal.
You will greatly enjoy a walk in Buen Retiro Park. There's a lake where you can go boating, wide avenues and narrow paths for strolling, canals and bridges, palaces, sculptures and fountains, a rose garden, and parrots hiding in the treetops.