Days like this I used to be so proud of the Finnish infrastructure. We've had -20..-30 C in Helsinki area, and down to -40 farther north. There have been delays in trains, 15 minutes or so (but yesterday Tampere train was hours late!). TV news interviewed kindergarten teachers who said kid are anxious as they had decided not to go out and play if it is colder than -15 and windy.
The adult things to do in this weather:
cleaning of the freezer. Food out to balcony, and when you take it bask, it's even colder than before.
ice lanterns - very ecological decoration for garden and graveyard