From the Heritage of Mercury: Almadén and Idrija World Heritage inscription:
The property includes the mining sites of Almadén (Spain), where mercury (quicksilver) has been extracted since antiquity, and Idrija (Slovenia), where mercury was first found in AD1490. The Spanish property includes buildings relating to its mining history, including Retamar Castle, religious buildings and traditional dwellings. The site in Idrija notably features mercury stores and infrastructure, as well as miners’ living quarters, and a miners’ theatre. The sites bear testimony to the intercontinental trade in mercury which generated important exchanges between Europe and America over the centuries. Together they represent the two largest mercury mines in the world, operational until recent times.
There are two sites in two different countries which are part of this world heritage site. Almadén, which is in Spain, and Idrija, which is in Slovenia.
I visited the property in Spain and this post will deal with visiting the mine in Almadén.
NOTE: There is no risk of mercury of poisoning in visiting this mine. Mercury in its liquid elemental form is very dangerous. However, you will not see any silverly liquid in the mine. The Mercury is in the form of Cinnabar, which is a red mineral created when mercury bonds with sulfur to create Mercury Sulfide (HgS). The only place you will see liquid mercury is in the visitor center, behind glass.
If you look at a map of the World Heritage Sites in Spain, Almadén sort of sits by itself, at least a 2-hour drive away from any other world heritage site. You could visit on a road trip from Madrid to Seville, but otherwise, you will probably have to make a special trip to visit. I drove out of my way to visit when going from Trujillo to Madrid.
Many people shy away from industrial heritage sites, but they are my favorite types. Learning how the items which made our modern world are an important part of our heritage, and visiting places like Almadén are an important part of that history.