Explore the Hidden Subterranean Passages

Beneath the limestone plateau of Laon lies a massive network of underground tunnels, quarry galleries, and military casemates known as the Souterrains de Laon. Originally excavated to supply limestone for building the medieval walls and cathedral, these cool caverns were later converted into defensive fortifications and air-raid shelters during World War I and World War II.

Access to the underground passages is strictly regulated and requires a guided tour booked through the Laon Tourist Office. Because the subterranean temperature stays around 12°C (53°F) year-round, bring a jacket or warm sweater even during summer visits.