Mercedes and Enrique's apartment is very well located, only 30 minutes from the airport on the express bus and a few minutes walk from both the main station in the area and the Reina Sofia. There are also lots of bus routes close by so it's very easy to explore the city from there.
The apartment is small, but neat and the beds were comfortable. Air conditioning works very well, keeping the place nice and cool in the night.
Shower works well and has good pressure, but there is limited amount of hot water, so you must be considerate of your friends/family when washing in the morning!
The apartment itself is on a main street, but is 4 floors up with no lift. Very quiet at night, but something to consider if you struggle with walking/climbing.
Mercedes was there to welcome us when we arrived and although she doesn't speak English and our Spanish is really terrible, we managed to understand the instructions about the keys, and how things work. There's a helpful list of recommended restaurants in the kitchen with descriptions in English so you can find places to get excellent tapas nearby.
Definitely try O Pazo de Lugo, their croquettas come in a huge portion, much too large for two people to share, but are so delicious, you'll try anyway! Have some vermouth, for an authentic afternoon tipple, Very good service too,
Overall, this is a great value apartment, clean, well located and with helpful but unobtrusive hosts. Looking forward to visiting Madrid again soon!