We had a visit to Luxembourg 3 years ago to look at iron mines.
Each country (France, Lux, Belgium) all have their national iron mine museums within a few miles of each other plus several good private museums and railways. Plenty to see for at least a week.
There is a rather nice slate museum/mine - Au couer de l'Ardoise here 49.81309,5.272887 on Google maps.
Les