Stephen Fry blogged about how imagination is not the same as fantasy. The latter is about making up a world never imagined before; the first, is about imagining yourself in somebody else's personal world.
I'm sure we've all sat on the tube, watching those around us and wondering about their story: does that frown mean that she's in a bad mood and, if so, why? Is he carrying a seemingly empty bag because he's got nothing to put in it, or is he expecting to fill it sometime during the day? The questions could go on and on.
Highrises are even better - you literally get glimpses into the space that people come back to, the place where they take off their shoes (at least we do in Sweden - we take our shoes off indoors), remove their makeup, the place where they let go of the day.
Sometimes you catch the silhouette of somebody preparing something in the kitchen, shadows in the bathroom window or moments when they seriously should've drawn the curtains.