Hong Kong Very shiny, clean and efficient subway system. It's remarkably easy to slide off the metal seats if you're not paying attention to corners.

Warsaw has a single line subway system. Bugger all use. The city council chose to have a Palace of Culture from Moscow instead when offerered a choice between that and a decent metro system.

London Underground is hellish. Useful, but foul. One of the oldest, one of the most run-down and underfunded in the world. But it's still my favourite zoo.

Paris is a confusing subway system, but, at least the old art nouveau station entrances are pretty. The tunnels are spooky.

the New York Subway is filled with stories.