Odessa catacombs is a huge network of artificial underground tunnels and labyrinths under Odessa and its suburbs, the length of which is now estimated at 2.5-3 thousand. Km (1500 – 1900 miles). One of the largest underground labyrinths in the world. For comparison: the catacombs of Paris reach 500 km (310 miles) Rome – 170 km (105 miles).
Most of the catacombs (95-97%) are former quarries where the building stones were excavated, since the 1830s. In 1860s, an extensive network of abandoned limestone mines appeared under the city. The system of catacombs also includes the caves of natural origin, exploration and construction pits, bunkers, drainage tunnels, storm sewers and other underground cavities.
Depth of quarries ranges from 4 to 30-35 m (13 – 115 ft). Some quarries are single-tier excavations, although there are two or tiered as well. Dimensions of the caves vary but on average they are of 1.8 m (6 ft) high and 3.5 m (12 ft) wide. The highest ones reach 5 m (16 ft). Maximum width – 5.2 m (17 ft). But due to landslides many passages became just manholes 25-30 cm (1 ft) high and 50-70 cm (2 ft) wide.
In fact, Odessa catacombs is a gigantic underground city with its avenues, streets, alleys, dead ends, areas, where until now the researchers discover new underground areas.