Very small, like the pictures show. Clean and has all the basics for a short stay.
However, the showerhead is broken and they put duct tape around it so it doesn't fit to the holder well and the angle is off. The shower is super small, I'm 1.87m so definitely on the bigger side, I had trouble moving in the shower, and hot water only lasts for 5 minutes or so.
Lastly, when I asked to book the Airbnb I informed the owner that I'll be arriving at 22:30pm, he approved the reservation no questions asked. The day before the flight I've been told I'd have to go someplace else in Madrid to pickup the key. So I had to pay extra for a taxi and roam the city after my flight with all my luggage.