Why are Soviet metro stations so deep?
Many underground rivers were discovered. It was safer to dig tunnels deep under the ground level. The depth of the tunnels usually ranges from 35-55 meters. Moscow metro was built not only as public transport. Why is St Petersburg subway so deep? St Petersburg does not have the best terrain to build a metro. The city is built on marshland. This makes the ground very unstable. That's the reason why the metro stations are located so deep, with an average depth of 60 to 70 meters.