The Odessa Catacombs are a network of tunnels that are on three levels, stretching out under Odessa, Ukraine and its surrounding region. The majority of the catacombs are the result of stone mining. The Catacombs reach a depth of 60 metres below sea level.
Most of the city's 19th-century houses were built of limestone mined nearby. These abandoned mines were later used and widened by local smugglers. This created a gigantic labyrinth of underground tunnels beneath Odessa, known as the "catacombs".