On 18.04.15 3:15, Nick Leverton wrote:
Opened in 1863, just a month after the Met line to Farringdon, the world's
second Underground railway was not a passenger line, but a private precursor to
the eventual Mail Rail system. And surprisingly linked to Mail Rail as well.
Worth a read on London Reconnections.

http://www.londonreconnections.com/2015/londons-lost-pneumatic-railway-the-worlds-2nd-oldest-underground/

Nick

There was one of them in New York City as well, AIUI.