Today in Gara (article in Basque language) they narrate a visit to the magnificient mines of Oiasso. It begins with the words that German engineer Wilhelm Thalacker wrote in 1803: Even four hundred men working for two hundred years do not seem enough to have digged all these mines.
The mines nevertheless have been in use for some two milennia, since the Iron Age until the 20th century. But the Romans did the most important and relevant work maybe around the 1st century CE; they digged some 50 km of tunnels in search of silver mineral. They also made major canalizations for leaking water (it rains a lot over here) to be evaquated from the galleries into huge lake-like water deposits. Their main tool was fire, which they used for illumination of course but also to break the rock.
The mines were finally closed in 1984 and nowadays the only people working inside them are archaeologists. They can be visited, according to the article, every weekday except mondays, in the morning and afternoon.
See also my previous post on these mines, that includes some relevant links.
Additionally, a secondary article (this one in Spanish, same webpage) that the mining area of Aizpea (Zerain, Gipuzkoa). These open mines are known to have been exploited for iron ore since the 12th century at least. The product suministered the many small foundries that existed in Western Gipuzkoa and that are at the origin of the industrialization of the area later on. More recently, in the late 19th and early 20th century it was exploited by a British company, until 1932, when it was acquired by a German consortium, eventually ending in the local hands of Patricio Echeverría that exploited them till their exhaustion in 1952.