Trotti aux Fosses

This is more or less the halfway point on the Fond des Vaulx route and here we find the most iconic karst phenomenon of all: the Trotti aux Fosses chasm, a vast collapse cavity (an underground space, the roof of which has gradually collapsed to the ground, Marche-en-Famenne Famenne-Ardenne unesco global Geopark 13 forming a huge well some 15 metres deep. The resulting limestone scree was gradually dissolved by the underground river beneath the Fond des Vaulx, accessible only to cavers.