I'm writing the review I wish I had read before booking this apartment. To all future travelers, I hope this is helpful!

Pros:
-Pol was nice and welcoming, and responded quickly to any messages we sent him.
-The apartment is really well designed to maximize a small space.
-Great location, very close to Plaza Serrano; many restaurants, cafes, and great shopping within easy walking distance.
-Nice private outdoor patios

Cons:
-The big sliding doors to both patios are in need of repair: one of them is detached from the top rail, and neither one of them seals even when fully closed (1/2" gap on one of them, 1" gap on the other), which unfortunately meant that all sorts of insects were able to get into the apartment, and we woke up with new mosquito bites every morning.
-The downside of the great location next to discos and bars meant that the apartment was VERY loud from 1 am - 6am, so we had to sleep with earplugs every night (see: doors don't seal).
-There was a steady line of ants going from one wall of the apartment to another
-WiFi is pretty slow - we rented a movie on our computer one night, but had to wait for 3-4 hours for it to download.
-There were no sheets on the bed when we arrived. There was a clean set available in the apartment, but they hadn't been put on the bed.

Overall, this apartment has the potential to be a comfortable spot in a great location if the necessary repairs are made, and provided that guests know to expect some noise due to the nightlife nearby.

Thank you Pol for hosting us.