Great apartment in the heart of Madrid. Very close to Madrid square and all the amazing restaurants. We walked everywhere from here. Hector is a great host. We had no issues with the Nuki app as others have written in their reviews.
The only minor issues is the lack of elevator and apartment being on the 3rd floor. After walking all day, I want an elevator to carry me. Not a big issue though. More than makes up for the great location. :-)