Comment Berlin is a small city? (Score 1) 625
Berlin/Germany had a tube based system for letters and postcards that extended to 400km in 1940.
It connected 79 post offices in the city and transported 8 million mailings yearly.
Destroyed in WW2 it was partly reconstructed and used up until 1986.
Article in German: http://de.wikipedia.org/wiki/Rohrpost_in_Berlin