Ask HN: Is there a good description of a physical implementation of Tor

I had a look at the description of TOR on https://www.geeksforgeeks.org/onion-routing/ and wondered if there was an equivalent for the sending of messages via physical or even mixed medium.

While it would be time consuming and requires reliable 'nodes' (people) it ocurrs to me that security would be even higher as there is no automation available for cracking letters.