The wild and desolate moors are set against the drama unfolding in the two houses. But as much as there is a nature versus culture theme going on here, Wuthering Heights (the house) is very much associated with nature, and so it can't really be put in neat opposition to it. As Lockwood explains at the novel's opening, "Wuthering" is "a significant provincial adjective, descriptive of the atmospheric tumult to which its station is exposed in stormy weather"(1.12). Translation: bring a jacket.
But the moors mean different things to different people. To Lockwood, the moors serve as a confusing expanse that's almost impossible to navigate on his own. The moors confuse him, especially when it snows. He sees them as "one billowy white, ocean" (4.101) full of pits, depressions, rises, and deep swamps. The boggy parts of the moors can mean death for some people. When Heathcliff imprisons Nelly and Cathy in Wuthering Heights, he spreads a rumor in Gimmerton that the two had "sunk in the Blackhorse marsh" and that he had rescued them (28.2).
But as much as the moors represent threat and menace, they are also full of mystery and mysticism. They are a source of comfort and a respite from the prison-like atmosphere of Wuthering Heights. To Catherine and Heathcliff, the moors exist as a supernatural, liberating, and boundaryless region. For them, the ultimate freedom is associated with wandering on the moors. They often describe their love and their own individual identities through metaphors of nature. Catherine's dying wish to be released on to the moors reinforces Heathcliff's analogy of Catherine as an oak contained by the strictures of Thrushcross Grange:
[Catherine:] "I wish I were out of doors – I wish I were a girl again, half savage and hardy […] I'm sure I should be myself were I once among the heather on those hills. Open the window again wide […]." (12.46)
Both Catherine and Heathcliff have an intense identification with the unruliness and brutality of nature. Catherine justifies her marriage to Edgar Linton using comparisons to the natural world:
"My love for Linton is like the foliage in the woods. Time will change it, I'm well aware, as winter changes the trees. My love for Heathcliff resembles the eternal rocks beneath a source of little visible delight, but necessary." (9.101)
Heathcliff's appearance draws endless comparisons to nature. It is "bleak, hilly, coal country" to Linton's "fertile valley" (8.53). Brontë does not set up a neat opposition between nature and civilization, though. First of all, life at the Heights is not exactly civilized; second, the very name of the house reflects its surroundings.
Like her mother, Cathy yearns to escape the confines of the house and play on the moors. Hareton slowly earns her trust by giving her a guided tour of some of the natural features of the surrounding countryside. "He opened the mysteries of the Fairy cave, and twenty other queer places […]" (8.85).