Great apartment! Excellent location in one of the major thoroughfares in Madrid. In spite of this, it is very quiet inside.
The apartment is big, even bigger than it looks in the pictures. The A/C works wonderfully, the bed is extremely comfortable, the shower is great, and the internet is fast and reliable. There were very minor issues, like one of the bathroom sinks was not draining properly. And the check-in was a little bit of a pain, since I had to grab the keys from a public locker that was at a 7 minute walk from the apartment, and dragging my large bag around was cumbersome. But I would absolutely stay there again, and highly recommend it.