If it's far too cold to go outside, try playing a game of hide and seek with your dog; you'll need to rearrange your furniture and create enough space as to eliminate any potential hazards that you or your dog might bump into in the heat of the game. Afterwards, try to hide away from your dog and encourage them to find you with their ears and their nose.
There are a number of creative and inexpensive dog puzzles that are sold both locally and online, so consider adding a few to your inventory for a rainy day (or several). Swedish dog toy manufacturer Nina Ottosson has created a menagerie of puzzles and toys for dogs of all breeds and all ages. These toys will really tease your dog's brain, so consider building up your pet's puzzle solving skills before trying this activity.