From 1897 to 1953, 27 miles of underground pneumatic tubes looped through the post offices of Manhattan (and out to Brooklyn). Letters too 15 to 20 minutes to travel from Herald Square to the Triborough post office, the northernmost in the system.

I’ve seen remnants of building-wide pneumatic systems, and knew that there was wider service, but never knew it was this extensive (of course, NYC was nothing compared to Paris’ 269-mile system).