Here area a few shots of the tow paths along the canals in France.

They were great because they were located between towns, not in towns, so they weren't clogged with people doing all sorts of different things, and holding up the cyclists. Occasionally they would go by a town, and you'd see a few more cyclists around, but the towns were small, and you'd be past the town in a few minutes.

You could also get up some speed because there weren't awkward intersections every few feet, and they were very clean ... I don't recall any broken glass, etc. on them.

If all bike paths were like that, I'd be much more inclined to ride them!