This is a simple flat with air conditioning, an excellent location, and comfortable beds
BEDS: 2x twin + 1 sofa, comfortable and with good pillows. Blankets were quite thin but even with AC the room was warm enough to sleep with them. The walls are a bit thin so expect to hear your neighbors.
BATH: clean and modern, with good water pressure. Shower got both hot and cold as desired. The shower door is a bit weird and it's hard to avoid getting water on the floor.
KITCHEN: small and not a lot of equipment. We didn't try to cook there, but found sufficient plateware for a simple breakfast. There are lots of healthy and vegan/vegetarian restaurants in the neighborhood, so we didn't feel like we had to eat in the apartment to get a healthy meal.
LOCATION: really nice. Easy walking distance to El Retiro, Plaza Mayor, Madrid Atocha train station, and El Prado. Lots of lovely restaurants.
HOST: Borja and Arnaldo were communicative and helpful, always providing detailed instructions and useful information. They couldn't accommodate our need to store our bags after checkout, but helped us find storage lockers.