One of Britain's longest cycle routes, NCN 6 runs all the way from London to the Lake District, via the East Midlands and Manchester. 

At almost 500 miles it's certainly not the most direct route, but a varied patchwork of railway trails, colliery paths, towpaths and minor roads, taking in several cities and large towns. 

There are unsignposted sections in London (follow the Paddington Arm towpath), across the Peak District into Manchester, and approaching Preston, where we've sketched out plausible alternative routes. There's comparatively few hills apart from in the Peak District, but you'll find a variety of surfaces.