5/5 stars for a phenomenal experience. Alfonso's apartment is clean, modern, spacious, and well situated right along Calle Gran Via. Our group of 7 people felt extremely comfortable in terms of space, and the patio was the perfect place to hang out on with a bottle of wine at night. The apartment's location is unbeatable, as it is only a 10 minute walk to the Palacio Real and Mercado de San Miguel and about 20-25 minutes to the Prado Museum.
Also, Alfonso is an extremely pleasant and accommodating host who was able to allow my group to drop off our bags early. His apartment exceeded our expectations and then some, and I would highly recommend anyone visiting Madrid to stay in Alfonso's apartment.