Alle-sur-Semois is a community in the province of Namur, 88 km south of the city of Namur and 27 km north-east of the French city of Charleville-Mézières. Much of the area is forested and there are many traces of former slate workings. Ardoi’Alle at Alle-sur-Semois offers to visitors a 45-minutes underground tour through large and mysterious chambers from which miners have extracted slate. Some discarded equipment is displayed and at the entrance a visitor centre provides a multi-media introduction to the geology of the area and the history of the mines.
Ardoi’Alle is linked through the organisation Le Réseau Ardoise d’Ardenne and the trail guide La Route d’Ardoise with similar slate museums at Bertrix in Belgium, Rimogne in France and Haut-Martelange in Luxembourg.