The U4 is one of six blast furnaces built between 1878 and 1904 by the Stumm brothers. During the visit, you will learn about its structure and history. The site is also open in the evenings, when it is set off by a light show designed by internationally acclaimed artist, Claude Lévêque: the huge iron monster turns the furnace red. At the foot of the furnace, 4ha of landscaped gardens known as the Jardin des Traces have been laid out on the former factory site.