Slightly off the point perhaps, but still I think relevant to this discussion, I vaguely remember seeing some TV programme on Channel 4 at some Godforsaken hour like 4am, that featured this guy who had made a lifelong study of disused tunnels in London, many of which are still accessible if you know how. To demonstrate this he walked from somewhere like Camden to Brixton entirely underground (Ok I can't recall the exact details but it was some way), the trip involved passing through at least one disused tube station (a rather eerie, ghostly place). Anybody else remember anything about this?