Not the best six, and definitely not a canon. Six that changed how I walk, which is a different and more useful criterion.
The list
Nan Shepherd, The Living Mountain. Covered at length elsewhere. The argument against the summit, and the best book here by some distance.
Robert Macfarlane, The Old Ways. Uneven, occasionally too pleased with a sentence, and containing perhaps four passages I have thought about every year since. The chapter on walking a tidal path is worth the book.
Rebecca Solnit, Wanderlust. The history rather than the experience — walking as a political act, as a right, as something that has been repeatedly enclosed and fought for. It is the book that made me notice who is permitted to walk where.
Werner Herzog, Of Walking in Ice. A short, strange, faintly deranged diary of walking from Munich to Paris in winter in the belief that it would keep someone alive. Not advice. A demonstration of what walking can be made to carry.
Iain Sinclair, London Orbital. Difficult, sprawling, and about walking the ring road around a city — the anti-pastoral entry here, and a corrective to the idea that walking books have to be about landscape.
Bashō, The Narrow Road to the Deep North. Three hundred and forty years old, about eighty pages, and the ancestor of every book above it. Read it last; you will see where everyone got it from.
What is missing
Five of these six are British or European and all six are by writers who walk by choice, in safety, with a way home. That is a narrow slice of what walking is, and I know it. Recommendations that fix this are welcome via the contact page — I have been sent three good ones already and am working through them.