Here are a couple of things we did when we were there a few years ago.

At Mammoth, we rented snow shoes, drove to the trailhead for Tower Falls and "hiked" to the falls. I stuck with the snow shoes. My husband hated them, took them back to the car and put on his Yak Trax. He did just fine.

We also walked all around the terrace area at Mammoth. Again using our Yak Trax.

At Old Faithful, we walked the boardwalk for hours. Again in our Yak Trax.

In case you don't know (I didn't until we planned our trip) Yak Trax are these spiral metal coils and rubber "soles" that you attach to your boots at the toe and heel. They're meant to give you added traction on icy or slippery surfaces and they really do. We wore ours on the sidewalks if they were iced, on the snow-packed boardwalks, and on trails that had been packed down by others. Took them off before going into buildings and in fresh, deep snow.

We loved Yellowstone in the winter. That's still our favorite of the 3 trips we've made there.

I walked the boardwalks at both places for hours also. At Old Faithful, I walked them for days and never tired of them!

I took a x-country ski lesson at Mammoth, which was excellent. The beginners trail is beautiful, even for hiking if you get tired of skiing. There are buses that will take you up there and back. Just be sure to check the times.

At Old Faithful, there's an easy, flat ski trail that runs along the geyser basin, and begins right at the Snow Lodge. There's a little ice skating pond at the Snow Lodge also.

A tip for those snow coaches -- up front with the driver is the most comfortable seat. They can get pretty bumpy.

We loved snowmobiling Yellowstone. They will outfit you in everything you need. We were out for hours and did not get cold.

When we saw the Snow Coaches the thing I remembered was how fogged up their windows were. I don't know how they could see anything!

I hope you will go back to Yellowstone in the summer. It is totally different. You won't be able to see or do a lot of things you do in the summer.

Thanks, folks. I'm excited to check out the hiking you recommend.

Floridafran, I previously read a post that recommended the YakTrax (probably yours) and recently purchased a pair. Very helpful tip.

Yes, someday when I can get a longer summer vacation, I should definitely see that version of Yellowstone (and Grand Teton too).

For anyone else traveling to Yellowstone in Jan-Feb, I recommend checking out the Frosty Fun pkg if you're staying in one of the 2 park hotels. If you stay at least 2 nights, for about $10 more than the cost of hotel and 2 snow coach rides, you also get breakfast & 10% off other meals and tours or rentals.