This is a walk for a soft grey afternoon. Three kilometres, five bookshops, and enough covered distance that a light drizzle won't put you off. You'll read more book spines than a casual browse requires and come out with at least one thing you didn't expect.
Start at Russell Square. The square itself is worth a lap — Bloomsbury's literary ghosts are thickest here, although you'd never guess it from the benches full of students on their phones. From the south-west corner, cut down Bedford Way towards Tavistock Square and your first stop: Persephone Books.
Persephone is really a publishing house that happens to have a shop. They reprint overlooked 20th-century women writers in matching dove-grey covers, each with a patterned endpaper chosen to match the book's mood. It is, I think, the quietest piece of confident publishing in London. Buy something you've never heard of; it will almost certainly be good.
From there, ten minutes through the Brunswick Centre to Skoob Books, which lives in a basement under the square. Everything's secondhand, the shelves are alarming, and a diligent forty minutes will get you three paperbacks for under a tenner. Skoob is where I go when I need to be reminded that reading is supposed to be cheap and slightly dusty.
You'll emerge blinking and make your way south to the London Review Bookshop on Bury Place. This is the opposite of Skoob: tightly edited, perfectly staffed, with a cafe that does what I consider the best cake in WC1. The front table is a better curator than most magazines.
Keep going south and you'll hit Foyles on Charing Cross Road, which is the loud chapter of this walk. It's a big chain bookshop now, but the building is beautifully done and the children's floor is worth a detour even if you don't have one. Finally, double back north-east to Marchmont Street for Gay's the Word, which has been going since 1979 and still feels, somehow, like a shop where something might happen.
Finish with tea in the Brunswick, or a pint at the Lamb on Lamb's Conduit Street if you've timed it right. You'll leave weighted down with paper and feeling, rightly, like you spent an afternoon well.