>> Another interesting fact was that you could walk from London to Kendal entirely besides canals
Well almost. Heading south, the Lancaster Canal used to go into Preston Docks, but the last mile or so of it has been filled in. From the docks traffic would then go down the River Ribble for a few miles before entering the River Douglas which was followed until a spur of the Leeds Liverpool canal could be entered at Tarleton Lock.
The link was re-establish about 25 years ago with a new stretch of canal round Preston, but the river parts are still used. You have to be a bit creative to follow the route on foot rather than the simple 'follow the canal' which will suffice for the rest of the way.