If I were to walk to work without using sidewalks, it would almost double my commute time! I've actually looked into it before - I always prefer finding alternative, scenic routes where possible - and there are some nice looking alternatives (although I wouldn't be able to avoid using sidewalks altogether), but they would take me quite a long way out of my way! Since my shortest route to work (using sidewalks all the way) is just over four miles, I'm not really very keen to extend this! Although I do sometimes take the bus, which is a nice quick way to avoid walking along sidewalks! ;D
I actually think it would be pretty much impossible to avoid man-made walkways anyway, even if I were to go through the countryside/woodlands areas. They are not untouched by man - they have their own little pathways and bridges that have been created so that people can navigate their way through!