Helmut's place is amazing!
The apartment is very close to the train station which makes it very convenient if you want to grab a cab or public transport. It has a few grocery stores nearby as well. Its around 15 mins by car to the center.
The best part about the apartment are the two huge terraces (each almost the size of the apartment itself). We spent all our waking hours in the apartment sitting on the terrace, eating, drinking, and watching the beautiful sunset over Barcelona.
The apartment itself is very well decorated and stylish. The only thing is that it might be a bit tight for four adults to stay there as there is limited space, and only one bathroom.
Highly recommend this place.