An hour's walk a day keeps the doctor away.
Mind you, here in Australia the doctor might be needed if the outside temperature gets above 35 degrees C.
Wintertime no problem. The trick is to vary the route for variety, and build a purpose into the activity if that helps e.g. walking to shops, do shopping and then home, or to and fro the library. Park the car an equal distance from some places which one needs to visit, do the round of visitations (no ghost apparel required), and save on petrol and parking fees.
I add ankle and arm weights (0.5 kg each) to add weight-lifting to the aerobic routine.
But not if swimming, kayaking or driving !!!