We enjoyed staying at Andrew's place. It was well located about 15 minutes (uphill) from Atocha station and 15 minutes from plaza mayor. It is also close to Retiro Park where you can rent out row boats. There are some lovely restraunts within a 10 minute walk such as Steakburger and Pizza Diablo.
Andrew's friends were there to greet us and also gave us a map and some dinner suggestions. The place was small but fine for a couple. The air-conditioning is thankfully very good.
On the downside, it's on the 7th floor which is terrible in the summer heat. There is currently construction for a lift which meant that there was a lot of noise from 8-1 and 3-7. I wouldn't return until the lift was installed. The bathroom floor was also flooded after each shower.
Andrew was really pleasant to deal with and very accommodating as we arrived and left late. He was available to give swift responses.
Altogether, we had a nice time in Madrid and in Andrew's flat.