Guillermo's apartment is in the hipster Malasaña neighborhood, which is pretty much in the heart of Madrid. We walked around and saw a good chunk of the city from here, and you can see a lot more much quicker if you use the metro, which is also really close by.
It has everything you need for a very comfortable stay, and Guillermo makes sure you get whatever else you might want.
The only issue is that it's on the 4th floor, so consider carrying backpacks instead of suitcases.
However, Guillermo met us at the entry and helped carry our luggage on our way up and down!
Guillermo also has excellent recommendations - do not miss out on them!
10/10 for the apartment and Guillermo!