The hill that rises to just over 500 metres in the Collserola park, Barcelona's "green lung", is one of the city's most famous balconies. Half way up is the Science Museum and at the top there are picnic areas, restaurants and an amusement park, with facilities dating from the early twentieth century. The Sagrado Corazon - the church of the Sacred Heart - that crowns Tibidabo is already an essential part of the image of Barcelona.