Speaking of rails and such -- getting around medium/long distances in London is dead easy on the tube.

SWMBO and I hardly ever bother with surface transport (buses, cabs) when we're in town, prefering to use our feet. And we do favour walking, as everything downtown is just so fascinating to us new-worlders.

A hike up the dome at St.Paul's is definitely cool, with great bonus views of The City in good weather.

Cheers