The place is absolutely perfect for a sightseeing trip! We walked everywhere in the center, and the train station Atocha (from which trains go to the airport) is also very close.
The apartment is very well equipped, despite the description it has everything you might need (towels, soap, kitchen basics, etc).
One important thing: the single bed is actually not in a separate room, but in an area next to the kitchen, it does not have a door. But this was completely fine.
All in all, a fantastic stay, thanks a lot!