PROS:
This apartment is in a great part of Madrid, and seconds away from Plaza Mayor. Although in a busy area, the apartment is not loud. The bed is very comfortable and the apartment has all the essentials you need for a short stay (bring your own shampoo and conditioner though).
CONS:
You have to WALK up FOUR flights of scary stairs to the apartment. If you travel light (like a backpack), and this is a short trip (weekend), then this place is fine. But we were there for 1 day in a layover on our way to another location for several weeks, and had several large, heavy bags. The staircase is narrow, steep and spiraling - making it exceeding difficult to haul luggage up, then down. I don't think we saw a mention of it being a 4 story walk up, otherwise we would definitely picked a different place to stay, even for day, given the difficulty we had taking stuff up, then down.
That said, the host was very accommodating and helpful in storing our luggage before check-in and after check-out, so that we could walk around the city without having to take our luggage with us. Again, if you travel with little to no luggage, and don't have trouble climbing stairs, this place is in a great location with lots to do and see in the immediate vicinity.