I've lived in several countries and thanks to being a designer I'm able to move and work in a new city every few years.
I'm listing two apartments, one in Barcelona and another one in Madrid.
The one in Barcelona has about 130m2 and it's located on a long, beautiful wide street where people love taking afternoon walks. Best of all it's right next to the metro station. It is simply decorated but you have all the facilities you might need. If you book a room, you'll probably see my father who will be staying there for the summer. He's a retired Japanese chef and he enjoys playing classical music on his guitar when he's not teaching at the community center.
The apartment in Madrid is where we spend most of our time in. It's about 90m2 and it's very centrally located. It's also very convenient as the metro station is at the end of the street intersection. My mother is based in Madrid and has been working as a local tour guide for VIP groups from Asian countries. She still works as such and so you might or not see her during your stay.