These magnificent waterfalls, which you can find pictures of on just about any scenery calendar, lie within the Grand Canyon of Yellowstone, where the Yellowstone river flows. Another feature is Mammoth Hot Springs in the northern area of the park. This is an area where limestone terraces are the major focal point. When driving down the road, you can't help but notice them because there are no trees. In the winter, you can view anything and everything within 3 days with no traffic and little congestion.
Many animals are out and the scenery is fantastic.
You can also go cross country skiing too. A good overall trip through Yellowstone should take you about 2 days or so to get everything in. Accomodations in the park are pretty expensive unless you just want to camp out. Reservations should be made 6 months in advance. Hope you had a wonderful time.