Marta’s place was lovely for our 4 days in Barcelona- it was perfectly located in a quieter part of the city but still walkable to numerous tourist attractions, restaurants, cafes, and bars. Artur met us and gave great tips on attractions to visit and how to get around the city using public transportation. The only thing I would note is that the elevator is more finicky than we expected based on earlier reviews. It was often stuck on a higher floor when we would get home, so we primarily walked up to the apartment. For two young adults who were fully able to climb 6 flights of stairs up and down multiple times a day, that was fine. However it definitely would be a challenge with big or multiple bags, or for those who cannot traverse stairs easily.
Other than that, the terrace and view of La Sagrada were unbeatable. Definitely recommend.