Members of the Guardian Angels volunteer anti-crime patrolers, 1981. On the NYC subway. Photograph by Christopher Morris.
15 Rare Photos of New York’s Graffiti-Covered Subway in the 1980s
Soundmap of London’s Canals
What is it like on the 'secret' Tube?
Empty Underground: lovely photos of the tube at its quietest
I’m Glad I’m a Boy! I’m Glad I’m a Girl!
The Open Country of Woman’s Heart

Why are Post-It notes the colour they are?

How to Make Love: A 1936 Guide to the Art of Wooing
London Underground ghost stations