Caves and potholes in Collserola - Pla de Barcelona

Collserola, which separates the city of Barcelona from Vallès, is one of the largest metropolitan parks in Europe and probably the most-trodden massif in Catalonia, given its proximity to the capital. Its relief, mostly granitic, nonetheless holds a number of cataloged cavities, evidence that karst is real there despite the very strong urban pressure of its surroundings.