Oscar Wilde set this play in his own time. His many references to particular political situations (the Suez Canal, Women's Liberal Association) made the play up-to-the-minute for his audience. A few years later you would probably have to look up the names to know what Wilde means.
What's important is this: it's turn of the century England; Queen Victoria is on the throne and London is seen as the center of the universe. England is getting rich off its colonies. Power and prestige in London mean international power and prestige. We can see the scope of Sir Robert's influence – and how the focus of his attentions shifts – by looking closely at the settings throughout the play.
We start in fashionable Grosvenor Square at a sparkling party full of international movers and shakers and the women who love them. Chandeliers, tapestry, and chamber music complete the picture. The Chilterns are wealthy and classy. The guests are on their best behavior. (If you want to party like a good Victorian, check out "Etiquette for the Ballroom," 1880.) Setting the first scene in such a public arena – even including characters who won't be seen for the next three acts – establishes Sir Robert's reputation and raises the stakes for his struggle.
The settings transition from this public arena to more private ones throughout the play – Sir Robert's morning room and Lord Goring's library. This transition echoes Sir Robert's conflict, and his willingness to sacrifice his career for his wife, if he must.
The morning room is a comfortable room with a fireplace and armchair. It's an appropriate venue for receiving less-intimate friends like Lady Markby and Mrs. Cheveley. Most of the philosophical debates happen in this room. It's where the hard work of changing minds happens, on the turf of our two serious characters, Sir Robert and Lady Chiltern.
Hard work of another kind happens at Lord Goring's place. Once we see three doors leading into the library, we know we're in for some fun hijinks. A staple of farce, multiple entrances create the kind of misunderstandings and missed connections that keep audiences laughing and plot resolutions up in the air. Once Lord Caversham, Mrs. Cheveley, and Lord Caversham are all tucked into the various pockets of this one small area, Lord Goring is motivated to think fast. He's the kind of guy who does well under pressure.
The last act returns us to Sir Robert's morning room, where everything is tied up in a neat comedic bow. The last moment of the play is its most intimate one. In the same spot where they fought bitterly over Sir Robert's past, he and Lady Chiltern are left alone to reconcile. Gentle with him now, Lady Chiltern remarks that "For both of us a new life is beginning" (4.297).