I spent several months in 2007–2008 working on a documentary about underground Moscow, and I can assure you there is indeed a Metro-2, plus a great deal else: large military bunkers 200 feet underground, VIP housing, evacuation routes, rail links with exurban command-and-control centers, and the like. This is in addition to the spurs of the regular Metro system, and the vaults, pedestrian tunnels, storm drains, and so on that have been dug under the city since mediaeval times (the area around Red Square and the Kremlin is supposedly honeycombed with tunnels). Owing to Moscow’s geology, there are also around 200 natural underground rivers flowing beneath the city with hollowed-out channels, caves, waterfalls, and pools. Homeless people, as well as fugitives and active criminals frequent (and sometimes live in) these underground areas. There is even a species of mutant rat that lives in the Metro; they’re not huge, as you’re probably thinking, but much smaller than normal. Rats, being highly-strung creatures, are placed under a great deal of stress by all the noise and vibration of the subway trains, and respond by producing just such offspring.