List some of the significant locations/settings in The Picture of Dorian Gray.

In The Picture of Dorian Gray, there are a number of settings which are significant because they reinforce the novel's key themes.

Firstly, consider Basil's studio. This setting, with its "rich odour of roses" and "heavy scent" of lilac, represents Dorian's innocence and youth, before he makes his supernatural pact to stay young and before he meets Lord Henry, who contributes to the corruption of his soul. It is interesting to note how the description of Basil's studio and garden reflect the importance of this meeting with Lord Henry: "The wind shook some blossoms from the trees . . . a grasshopper began to chirrup by the wall." This coming-alive of nature is symbolic of the impact which Lord Henry will have on the young Dorian. 

Secondly, Dorian's old schoolroom is an important setting in the novel. This first appears in Chapter Ten and evokes memories of Dorian's "lonely childhood" and the "stainless purity of his boyish life." The schoolroom thus symbolises repression: Dorian represses the painting from public view, so that his secret pact will never be revealed, just like he has repressed the painful memories of his childhood.

Finally, the opium dens, which feature in Chapter 16, are significant because they represent the corruption of Dorian's character and his soul. The opium den is the epitome of Dorian's hedonistic lifestyle and his selfish pursuit of pleasure. This idea is supported by the description of Dorian as he roams around:

Callous, concentrated on evil, with stained mind, and soul hungry for rebellion, Dorian Gray hastened on.

In other words, the opium dens transform Dorian, and he becomes just like the painting that he has tried so hard to conceal.