The Inland Sea, by Donald Richie. Not about Takayama specifically, but Richie's masterpiece of post-war Japanese travel writing is the right tonal preparation: an unhurried, sympathetic, slightly melancholy account of small-town and rural Japan, written by an outsider who came to know it better than most insiders. Travellers heading into Hida do well to read this first.
Memoirs of a Mountain Hermit (Hosshinshu), by Kamo no Chōmei. The 12th-century Buddhist hermit's reflections on impermanence and the rural mountain life echo strongly in the temple groves of the Higashiyama walk and the cedar shrines around Takayama.
Snow Country, by Yasunari Kawabata. Kawabata's Nobel-winning novel of an affair in a snowed-in mountain inn is set in nearby Niigata, but the atmosphere it captures — the way mountain Japan turns inward in winter — is exactly what Takayama feels like under a foot of snow.