The main thing about this apartment is its location in the middle of a very busy shopping/hotel area. This has many advantages in terms of enoying yourself in Madrid. You can walk to the most famous museums, to films, to the opera, to flamenco, to neighborhoods that are picturesque or touristy or rich or bohemian, sometimes all at once. Shopping, restaurants, entertainment, it's all RIGHT THERE. A very large and connected metro station is 100 yards away. Supermarkets, pharmacies, and "bazzars" (the equivalent of dollar stores) are quite close.
Things to know: the apartment is quite small. It works well for one person; maybe two if you're used to close quarters. And the other thing is that because it's in the center of everything, the street noise can be quite lively at night and sometimes until dawn. You must bring earplugs if you want to sleep.
Highly recommend walking through the adjacent neighborhood of Malasaña.