One of them shows Las Médulas. Las Médulas is a cultural region in northern Spain. For two centuries the Romans exploited the gold deposits by ruina montium, a type of hydraulic mining which involved undermining a mountain with large quantities of water. It was the most important gold mine in the Roman Empire. When the Romans withdrew, they left a devastated landscape. Las Médulas are since 1997 on the UNESCO World Heritage List.
Rural Architecture (from set of three) (issued 10-10-2016)
Thank You very much Belén!