The Belgian mine site famous for a mass burial of Iguanodon skeletons is Bernissart. The discovery began in 1878 in the Sainte-Barbe coal mine, where miners encountered fossil bones about 322 meters underground.
The bones were initially mistaken for pieces of wood containing gold because many were coated or filled with pyrite, commonly called fool’s gold. A large-scale excavation followed, lasting several years and uncovering around 30 remarkably complete skeletons, with some accounts recording at least 38 individuals or partial individuals. Most belonged to Iguanodon bernissartensis.
The find transformed dinosaur science. Louis Dollo studied and reconstructed the skeletons, and in 1882 one of the first complete dinosaur mounts was assembled in Brussels. The animals were originally displayed standing upright, reflecting nineteenth-century ideas about dinosaur posture; modern reconstructions show Iguanodon spending much of its time walking on all fours.
Bernissart is a town in Hainaut, western Belgium, near the French border. Charleroi, Liège, and Brussels are Belgian cities, but they are not the mine site named in this question.