Odesa catacombs
The Odesa catacombs (Ukrainian: Одеські катакомби) are a labyrinth-like network of tunnels located under the city of Odesa and its outskirts in Ukraine, that are mostly (over 90%) the result of stone mining, particularly coquina. The system of Odesa Catacombs consists of a network of basements, bunkers, drainage tunnels and storm drains as well as natural caves.