The Pre-au-Tonneau Cave

Visible below the RAVeL, this cave impresses with its massive entrance arch, formed by the collapse of a rock wall. Once a main sinkhole for the Lhomme River—before being cut off by the railway embankment in 1880—it still channels underground floodwaters down to a deep sump. The Pré au Tonneau cave is a key link in the Calestienne's fascinating underground water system: the waters of the Lhomme and Wamme rivers vanish into these limestone passages, travelling underground for five days before reappearing 4.2 kilometres away at the Éprave resurgence.