That's really something Paul. [Linked Image]
I saw a documentary on DW TV about a year ago about an underground network, in Germany, run by compressed air, to send mail and other stuff in sealed containers between buildings, but I've never heard anything of it since.
Apparently, there also used to be a system used in the UK in multi-storey Commercial buildings that used a Vacuum system to transport money and other things between floors, have you ever heard of this?. [Linked Image]