The Chełm Chalk Tunnels are a system of tunnels dug into the chalk under the city of Chełm in eastern Poland. The tunnelling began in the Middle Ages for chalk mining and was discontinued in the 19th century. The underground tunnels also served Chełm's inhabitants as shelters during raids, wars and pillage. The system is now open solely for tourists. In total, the network of tunnels stretches for around 15km.