Wonder at the remains of a Roman gold mine in Northern Spain
While this spectacular and strange landscape seems natural, it's anything but. The undulating green and red clay scenery is the direct result of Roman-era gold mining using a technique called ruina montium (collapsing mountains) wherein massive amounts of water moved via aqueducts were pushed through hollow spaces in the mountains--eventually turning them into rubble.
You're best off reaching this particular attraction by car or bike. Another option is taking the train to Ponferrada and a taxi to the monument (30 minutes). Nearby Airports include León, A Coruña and Vigo (León is closest).