My fiancé and I rented from Nader's Gran Vía/Callao condo in Madrid. We would highly recommend both the condo and renting from Nader. Nader was communicative, punctual, and incredibly welcoming. He walked us through all the details of the condo as well as helped us understand the surrounding area. He was a pleasure to get to know and work with.
In terms of the condo itself, it was very clean and well-kept, and includes all the amenities you need for a stay in the city; it is truly a quiet space as well despite being very centrally located in the city. The best of both worlds!
Lastly, we would recommend taking up Nader's offer of a pickup car service from the Madrid airport. Nader's friend, Jose, met us right at the terminal and gave us a lift directly to the apartment. He, too, was very friendly and punctual, and gave us some awesome recommendations to visit during our stay. The cost was also very reasonable.
Could not have worked out better. We look forward to staying with Nader again.