Pol Y Maria's spacious apartment has the most incredible view of the city, the best you will find. You can watch the sunrise AND sunset on the spacious terrace and even get a suntan because you are on the top floor. The metro station is just a couple minute walk away and it is always easy to catch a taxi out front of the building. The Gracia neighborhood is only about a 15 minute walk away. It is the perfect place to be just outside of downtown yet still feel like you are in the city.
Make sure you check that the hammock is available! As a solo traveler, it was a great. But if you are coming with a group, make sure you understand all the rules and $$extra charges. They are a bit complicated and hard to understand.