So 2012 is set to be the wettest British summer in 100 years. Fortunately, London has quite a collection of underpasses, covered walkways and arcades to help damp denizens get around town in miserable weather. But what's the longest journey you can devise that makes use of covered walkways? Some rules:
1) No passing through ticket barriers or other gated restrictions.
2) The whole journey must be under shelter of some kind: you can include building overhangs, tunnels and arcades, as well as enclosed public spaces like shopping centres that require no entrance fee or ticket. No umbrellas or portable shelters, obviously.
3) No doubling back along the same route.
4) No use of transport. Walking only.
We'll put forward the Woolwich Foot Tunnel to kick things off, supposedly 504 metres long. If you want to measure your idea, use the 'create map' feature on Google Maps, which includes a line-drawing tool.
Oh, and feel free to suggest useful and little-known sheltered routes, even if they're not very long. Maybe we'll do a map.
Other London puzzles: