The periods in which the numerous galleries extending under Tellure park were dug are recognizable by their shape. In the Middle Ages, they were shallow, rounded, and low in height. Their hard gneiss walls still display multiple traces of chisels' impacts. In the 16th century, miners from Saxony brought innovative techniques that allowed the galleries to be wider (1.64 to 2.30 ft / 50 to 70 cm) and higher (6 ft / 1.80 m). They are slightly sloping to drain underground water. The digging of the 18th and 19th centuries were performed with explosives and later electric tools.