Resurrect Dead: The Mystery of the Toynbee Tiles

The rise of the internet in the 1990s suddenly gave people the ability to talk and form communities about all kinds of weird niche hobbies and mysteries that, as isolated individuals, they previously had to muse over in silence. One of these, I remember, was the "Toynbee Tiles", linoleum squares left on the streets of Philadelphia over these years that contained the cryptic message "Toynbee idea i...