Alfred Wainwright, A Pictorial Guide to the Lakeland Fells: Book Five — The Northern Fells — the indispensable hand-drawn guide to every hill above Keswick. Wainwright walked, drew, and wrote each page himself in the 1950s and 1960s; his terse prose and beautiful maps are still the best way to plan a walk on Skiddaw or Blencathra. Buy the pocket-size revised edition before you set off.
Hugh Walpole, Rogue Herries (1930) — the first of the Herries Chronicles, set around Borrowdale in the 18th century, by a long-resident novelist who lived above Derwentwater. A romping, melodramatic family saga that ties the landscape into deep historical fiction.
Norman Nicholson, The Lakers (1955) — the Cumbrian poet's elegant and slightly grumpy history of how the Lake District came to be seen as picturesque, and what that did to it. The best short introduction to the literary and cultural shadow that hangs over Keswick today.
Sarah Hall, Haweswater (2002) — set further south but indispensable for understanding modern Cumbria: the drowning of Mardale Green to make a reservoir for Manchester, told as a love story. Hall's prose is as taut and exact as a slate wall.
Beatrix Potter, The Tale of Peter Rabbit (1902) and Squirrel Nutkin (1903) — both written here, both set here. Squirrel Nutkin's island in particular is St Herbert's, in the middle of Derwentwater.