Anyway, I rediscovered the application over Christmas. After I'd thrown it away and started again from scratch, I had a web page that could generate random walks, beer-glass walks and even themed walks (of which pub-crawls would be the canonical example, but you could do church-crawls or even Dixons-crawls if you really wanted to).
The user interface is appalling, and I make no claims for the code, other than "if you think that's bad, you should have seen version one", but it seems to more or less work. Try it out for yourself. Oh, and if it auto-generates you a suicidal walk: say "down the M4, across a minefield and then over a cliff", I disclaim all responsibility.