Fortunately for me, I have very clever friends, and I've been asking them for examples of upcycling that they've come across. This comes from Pip:
“I did read this about London bollards (in The London Companion p77, published by Robson Books 2004 and edited by Jo Swinnerton). Those erected in Georgian times were mostly, and enterprisingly, made from disused cannons, with a defunct cannonball blocking the mouth, in the reverse process to melting down iron railings to make weapons.”This led me to march all around my SE1 neighbourhood, photographing examples of bollards: modern ones meant to look like cannon, old bollards designed to look like old cannon, and old bollards that I think are actually made of old cannon and cannonballs. Within an afternoon, I'd become slightly addicted to this example of necessity giving birth to reinvention, only for the reinvention to later take off in unexpected directions of its own.