Let me start my review with a single comment - the location is just perfect. It is really one of the best locations you can find on Airbnb in Madrid. You'll be near all the museums, the Retiro Park, Atocha (for traveling to and from Madrid), gyms, restaurants and you have a Mercadona literally next door to the building (the only bad part is that you'll hear the supermarket's door opening and closing all day when it's quiet).
The apartment itself is not the biggest but is just great, and has everything you need. Shower is excellent. Plenty of storage space. Bed is super comfortable, with an air conditioning that will keep you cool and keep any noise from disturbing you.
Kitchen is tiny, uncomfortable. The microwave is a bit too high (and I'm not particularly short), meaning you may have accidents when pulling food out, especially liquids.
To dry clothes, you will need to hang them in the bathroom, as there is no exterior space. Kind of a downside, but with the summer weather you can easily dry clothes in a few hours, and Maximo has installed a heater for the winter.
The only big problem I found with this apartment was having to pay for fiber internet, as the connection I found upon arriving was too slow. I didn't complain about this once, but I found it unfair (and the only host in Madrid who has done this).
All in all and leaving the internet aside, my favorite of 3 Airbnb apartments in Madrid. Recommended!