I usually don't write long reviews, but this apartment needs one for future visitors.
The good parts:
Location is great, within walking distance of most interesting things Madrid has to offer.
Easy to find, close to subway and other transportation means
Closets are extra-large, so you can actually unpack properly
The bad parts:
Pictures have been taken using lens that make the apartment bigger than it is (this was completely pointless, as the apartment is big enough, but it gives you higher expectations only to be slightly disappointed afterwards)
Bathrooms are small and one of them smells mouldy
Bedrooms are a lot smaller than pictured
Terrace needs new furniture, the current one is old and broken; the floorboards are broken or not properly secured with screws
Oven was not cleaned; kitchen hood is noisy and old, barely does anything
The kitchen is actually the hallway, so you enter directly in the kitchen
Biggest bedroom is actually in the basement, and is not heated properly.