First things first: This apartment is all you will need for a romantic stay in Madrid.
After that, there is not much to tell you that you cannot read in the other comments.
The apartment: has everything (and we do mean EVERYTHING) that you need. Also note that the apartment is at floor-level and you step directly into the apartment from the streets. We were a bit concerned about the safety of this, but after seeing the massive iron door, this quickly disappeared (even if you have the key, you need practice to get in).
The area: is very nice and quiet, and has a lot of small shops and restaurants close by. There are no bars within 50 meters of the apartment, making it very quiet at night. But within 400 meter you will have a wide array of bars and restaurant to choose from.
The host, Mariano: is very good at giving advice and suggestions. We actually never met him, as he was traveling, but he arranged for a friend to give us the keys. We never had any problems.
Good advise: remember to bring slippers, the bathtub can contain two adults at the same time, and the apartment has two giant wine glasses! Prepare to have an awesome time!
The best regards:
Mathias & Julie