The Grand Union Canal runs for 147 miles from Paddington right into the heart of Birmingham. As it links the two biggest cities in Britain it was a major transport link before the coming of the railways, although nowadays it is almost exclusively used by pleasure craft.
I walked the Grand Union Canal in sections between 1999 and 2001, extending it slightly by adding the Regents Canal from Mile End in East London to the southern end. The walk passes through some pretty countrysde, and even when going through cities or towns it keeps a rural, attractive air. The walking is easy with no significant climbs and a generally good towpath underfoot, which makes it an ideal training walk for long-distance walkers.