If you want to see a wonderful view of the entire city, without being surrounded by people, this is the perfect place. It is also a very charming place, was a former anti-aircraft bunker during the Spanish Civil War, is pretty dilapidated but retains the essential structure.
It is a charming and welcome green space in the heart of Barcelona. It has water displays including a beautiful fountain and small lake along with lots of grass verges to lie down and soak up the warm sunshine. A great spot for relaxation, a walk... the place that I like the most is a glass building full of plants inside.