This is a lovely apartment in a set of apartments with its own outer security door, with a shared laundry room. The apartment is quite beautiful, and we were met at check-in and shown around the apartment. If you're a Rick Steves fan, the apartment is at the north end of the tapas street Calle Cava Baja, and is just a few minutes walk from Plaza Mayor and the Palace.
The only minor drawbacks are 1) it's a bit noisy outside the apartment, since it's a corner unit on a big restaurant street. But honestly, I think any apartment in the center is going to be a noisy - you're in the middle of a major city. 2) The wifi in our unit was pretty terrible - kept going in and out, making it difficult to stream music. But I would still rent this unit again, given the location and the quality of the unit.