Recently I visited the Congost De Mont Rebei, in Sant Esteve de la Sarga (Pallars Jussà), near Lleida, Catalonia.
It has to be one of my favourite places I have visited so far, and it has the most stunning views of the landscape.
The path up the mountain is amazing, as you are walking on the edge and into the mountain itself.
For the more adventurous types, you can try kayaking int he river below and rock climbing.
You can also see pre-roman ruins from the 5th to the 9th century.