The Doctor and Donna in “The Unicorn and the Wasp”

[Stepping out of the TARDIS] Ah! Smell that air! Grass and lemonade! And a little bit of mint. Just a hint of mint. Must be the 1920s.

You can tell what year it is just by smelling?

Oh, yeah.

Or, maybe, that big vintage car coming up the drive gave it away.