I was recently in San Francisco, a walker's town, though only for those who like a bit of intense aerobic exercise as they plough up the killingly steep inclines. I'm not sure I enjoy it exactly but I tell myself it must be doing me good. And of course once you get the lay of the land you do become able to find routes that leave out the worst of the ascents. I'm better than I used to be, but I still find I'm the only person pounding up streets that everybody else is walking down.

One way y...