Spent a couple of hours on Sunday walking some of the little alleyways of the City of London, the kids were keen to explore more of the "secret" ways after seeing a few last week. OSM was by far the best for route planning, even the A to Z doesn't make it clear at a glance which of the various courts and lanes are pedestrian only, whereas OSM clearly shows paths and steps distinct from back streets.
Only found one new alleyway right near Bank and rain stopped play earlier than we'd planned, but it was still great fun.