A manganese mine newr Riw in the lleyn peninsula. Was worked during the second world war for the manganese which was used for strengthening steel for armour plating tanks etc. Two hundered men worked there at that time.
Mine has been filled in, but a remains of a steam boiler and an incline drum remain on site. A very interesting book called' The Lleyn Penuinsula Mines' by Wil Williams 1995 is worth reading.