Here's a nice, short pictorial from Time magazine on the busy after
hours happenings of London's subterranean railway - not a great deal
of textual description, but that's not really the point of such
things:
http://www.time.com/time/photogaller...823147,00.html
(Spotted on the DD forum.)

I must say that I'm always rather intrigued by the high-vi bedecked
army of workers I see on the other side of the escalators descending
for a night's when work I'm coming out of the Tube late in the
evening.

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(p.s. There's a number of points being raised in some of the current
threads that I really want to respond to, in particular regarding
Oyster PAYG, and also ELLX - I'll get round to doing so when I can.)