My 2 colleagues and I worked at an art fair close to the Prado Museum, which is 17 min walking distance and stayed for a whole week. The apartment is nice and although it is rather small, we found it to be cozy. It has everything we needed, a coffee maker, hairdryer, cleaning products, washing machine, microwave, etc. There is no lift so if you have a heavy suitcase, you have to carry it up 2 stair cases. The apartment is on the interior side of the building, meaning there is no view, but the upside is that it is very quiet.
The neighbourhood, Lavapies, is very close to the main train station Atocha and many metro stations. As an all female group at night we were ok, but its definitely not the poshest neighbourhood of Madrid and I definitely felt like I had to watch my things, especially at night. There is a 24hr supermarket just 5 min away, which is nice and many bars/small diners to have breakfast or a meal as well.
Cipri is a wonderful host, as has been mentioned many times before. He goes out and beyond to make you feel comfortable and was just so nice. His suggestions for dinners, shows, grocery shopping, etc were perfect. Thank you for making us feel at home in Madrid Cipri!