It is located a few kilometres from Ponferrada, beyond the lake Carucedo is Las Médulas, natural wonders indeed - created by the Romans, who dug gold. 60,000 slaves for 250 years had produced 1,650,000 kg of gold (5,000,000 Roman pounds). They led the water through canals, which were dug up and hence arose incredibly bizarre landscape of jagged mountains, caves and ravines.
It is wonderful, incredible to see it. But more incredible is that it is the people who made it, poor slaves, but diligent Romans and theirs architects :).
I must confess that we never were coming up to have all the view before us, because it was so warm and unfortunately I had my sciatica and therefore a little difficult to go. But I want to come back some day and do this trip at finish :).