Moscow.
Busiest
which city has underground railway system streatching 265kmand 170 station
Subway.
Kolkata
Both as a bomb shelter and a nuclear radiation fallout shelter. OR... The Busiest.
London, UK in 1863
The metro train, or underground train system, was invented in London, England. The first underground railway, known as the Metropolitan Railway, opened in 1863, connecting Paddington and Farringdon. This innovative transport system paved the way for similar underground systems in cities around the world.
The Paris Métro is an electric underground railway system; the term metro is also used in other countries to define a rapid transport system, not necessarily underground.
The system was labeled "The Underground Railroad", but obviously was neither a literal railway, nor technically underground.
the busiest.
Madhya Pradesh