Bordered by wood and featuring a steep terrain, On is one of the most picturesque villages in the Wamme Valley and boasts several remarkable buildings. The proximity of the railway and the Gerny plateau facilitated the development of agricultural activities and the exploitation of a significant quarry. Together with Jemelle, Rochefort, and Han-sur-Lesse, the region of On is one of the most interesting in Belgium regarding underground hydrology, as three rivers (the Wamme, the Lesse, and the Lhomme) have significant underground flows and carve out vast complex reservoirs. On, one of the most picturesque sites in the Wamme Valley, features several remarkable buildings from the 18th and 19th centuries, such as the former Toussaint farm, a U-shaped blue stone dwelling by the river. The village suffered extensive destruction during World War II.

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