The Willows

Two friends, the narrator and a tough, practical Swede, are canoeing down the flooded Danube beyond Vienna and Pressburg, and camp for the night on a small sandy island among endless swamps of willow bushes in the middle of Hungary. As the wind blows and the river rises, small, strange things begin to happen: the willows seem to move, a paddle disappears, holes appear in the canoe, and the two men become convinced that they have strayed into a place where another world touches ours.

Algernon Blackwood (1869–1951), an English writer who loved wild places, published the novella in 1907 in The Listener and Other Stories. H. P. Lovecraft considered it the finest weird tale in English literature, and its horror comes from what is never shown. Worth reading alongside it: Lovecraft's The Call of Cthulhu.