Javier was an excellent host and replied immediately (within minutes!) whenever I asked him a question via text. He was very helpful, welcoming, and amenable. The apartment is modern and cozy with lots of natural light and an elevator in the building. AC, heat, small equipped kitchen, washing machine, TV, and WiFi are all provided. It is located in the absolutely best central neighborhood of Madrid (Salamanca), and is in short walking distance to museums, cafes, restaurants, parks, tourist sites, metro and bus stops, shops etc. You can easily catch a taxi on the corner of Castelló and Alcalá within a couple of minutes. The street is quiet and residential even though it is steps away from a major thoroughfare (Calle de Alcalá). It is less than a 5-minute walk away from the Retiro Park, for a quick walk or run in the morning. For breakfast or lunch, there are lots of informal cafés and eateries within a 3-block radius.
Highly recommended as a base from which to explore beautiful and exciting Madrid! I would definitely like to stay at this apartment again on my next trip to Madrid.