The apartment was very clean, well equipped and the location is excellent. There's a super market right next door, the Palacio Real and the La Latina metro station are both about a 5 min walk away from the apartment. Also, be sure to check out the San Francisco el Grande right next door, it's one of the prettiest/flashiest churches you'll find anywhere. The only downside about the apartment is that the soundproofing is quite terrible so be sure to pack earplugs if you plan to get enough sleep.
Marcos was a very friendly host and overall we enjoyed our stay in Madrid.