The hosts: I have to start with them because they were so responsive and flexible. They answered every question immediately, provided lots of useful advice, and went above and beyond in accommodating our check-in time. Check-in was a breeze and they were so pleasant throughout.
The space: modern, immaculate, comfortable, nice building, excellent location. Comfy beds and nice bathrooms. The bedrooms are separated by the living room, which provides a nice amount of space and privacy especially for friends/couples traveling together. Aside from normal apartment building sounds, it's dead quiet and there is absolutely no street noise (a big deal in noisy Madrid). Very safe neighborhood. There are a ton of excellent restaurants, bars, cafes and stores all around, as well as convenient grocery and bakeries. Museums, Retiro Park and subway are an easy 5-10 minute walk. Atocha Station is about 15 minutes, also an easy walk. This is a perfect place to enjoy Madrid--highly recommended!