Olivia’s house is isolated from intrusion.

When she first meets Viola, Olivia says, I heard you were saucy at my  , and   your approach rather to wonder at you than hear you (I.5.161–3).

Ask yourself: How significant is it that the last scene of the play takes place not in Orsino’s palace but in Olivia’s garden, and that every character is now within the walls of the estate?