"If the Wild Wood ... symbolises the darker side of human psychology, it also has a place in that layer of The Wind in the Willows which examines the proper and improper role of Imagination in the individual's life. Here, it seems to stand for the tangle of rich and dangerous symbolism which threatens the mental life of even the most sober of artists. The image is not unusual; for example, Charles Williams used the wood Broceliande to carry just this meaning in his Arthurian cycle of poems, Taliesin through Logres. Williams described this wood as 'a place of making', from which either good or evil imaginings may come, and so it is with Grahame's Wild Wood.
The most striking fact about the Wild Wood is that, despite its threatening nature, Badger dwells at the heart of it; and Badger is the most wise and perfectly balanced character in the book, with his gruff common sense, his dislike of triviality (he chooses to come into Society only when it suits him) and his strength of character which can - at least temporarily - master even the excesses of Toad. Badger is, of course, a certain kind of English landed gentleman, but he is far more. He is the still centre around which the book's various storms may rage, but who is scarcely touched by them. He is, one may surmise, the deepest level of the imaginative mind, not easily accessible; perhaps he stands for inspiration, only visiting the artist when it chooses, and then behaving just as it wishes. 'You must not only take him as you find him, but when you find him,' Rat says of Badger. Above all he is not to be sought out deliberately: 'It's quite out of the question, because he lives in the very middle of the Wild Wood.' The deepest level of the imagination dwells (as surely it must) right in the middle of spiritual or psychological danger."
From Secret Gardens: A Study of the Golden Age of Children's Literature by Humphrey Carpenter.