This place is amazing! Really beautiful and clean spot in the mountains. The view from the roof is incredible and had a few really nice late mornings laying in the sun on the roof overlooking the view. The apartment is spacious, cute, and very well-kept. Beatriz was great, and had a few friends helping us settle in since she was out of town. Her friend let us in (even though we got in really late) and had bought us some snacks which was really sweet.
The train is a few minutes walk from the house and goes straight to Barcelona city center. It is about 20 minute train ride from Las Planes to the city center. On Saturdays the train runs until 2am, but on weekdays it only runs until 12:00am. It is hard for Taxi's to find the location, and is a bit expensive, so I would plan on trying to take the train back. I would also recommend getting in touch early if you land very late at night, was kind of hard to coordinate. But, we left at 3:30am and Beatriz was helpful and called us a taxi that was on time.
Beatriz gave us a lot of great recommendations for food close by (would 100% recommend Font de Las Planes, very short walk from the residence).
My only regret is not spending more time in the mountains near the air bnb, so beautiful.