Some years ago, friends gave us this lovely cast iron simmerpot for Christmas. In goes a stick of cinnamon, a handful of cloves, little twigs snipped of a fir or similar tree and an old apple or orange, sliced. Fill up with hot water.
Bring to a boil, then reduce the heat as low as it will go, keeping the pot at just a simmer. Your house will smell amazing. While this pot looks lovely, any old pot will do. If you have a wood burning stove in the house, just place it on there.