I suggest fellow travelers seek out one of the many other options in Madrid. We had a disappointing and unprofessional experience in trying to resolve a problem with this host, but otherwise, this is a great apartment. Thankfully, AirCover provided some protections for trip.
The pros: The apartment is incredibly unique, charming, and well-located on a quiet street. The hosts were communicative and enabled us to have an early check-in. The hosts were able to secure an alternative, though lesser, option after a key amenity (air conditioning) broke.
The cons: We specifically sought an apartment with air conditioning during a heat wave. We found that the air conditioning was broken; we spent the first night sleepless. Since it was a Sunday, there was no option to have someone repair the air conditioning that day, and no guarantee that it could be fixed during the duration of our trip. The hosts identified an alternative AirBnB with functioning air conditioning, and we opted to move our items mid-trip rather than cancel the booking altogether. The alternative AirBnB was very different from the experience we had originally sought, and cheaper per day. We requested a refund for the first night with broken air conditioning, as well as for the fare difference between the two AirBnBs. The host's reply was both unprofessional and belittling: "Traveling costs money and you have to pay for it"; "I live in Madrid and I do not have air conditioning, and I survive and also do not contaminate the planet"; and "I would have returned something for the inconvenience of the first night, but the truth is, after all our effort, I don't feel like it."