For anyone interested in the City of Moscow, this is a must read: 

What is hidden under Moscow? This question has intrigued Vadim Mikhailov since he was a child in the early 1970s, when his father, who drove a train in the Moscow subway, first gave him a ride in the driver’s cabin and showed him the network of Metro tunnels beneath the Russian capital. By the time he was 12, Mikhailov and his friends had begun making increasingly ambitious journeys beneath the city.

Discoveries began with the first expeditions. Through manholes and building basements the boys wriggled into labyrinths under the Russian capital. First, they explored the bomb shelters under Leningradsky Prospekt, then they came across an Academy of Oceanology warehouse. “Imagine walking along endless corridors,” recalls Mikhailov, “something dripping from the ceiling, the uneven light of torches. And all of sudden you find yourself in a room full of tanks of formalin, containing various sea monsters.”

They soon went deeper underground. According to Mikhailov there are about six levels under Moscow, and in some places as many as 12, including old sewer systems, fountain foundations, and sloping drainage tunnels entangled in the depths.

Read the whole thing.  Fascinating stuff.