If you are travelling from Denver make a little detour (Hwy 36) and visit Boulder,Colorado. Boulder was also named as "8 Fabulous Winter Wonderlands" and "Top 10 Healthiest City To Live and Retire." It is nice little collage town in foothills of Rocky Mountain. Hustle and bustle of students of University Of Colorado. Beautiful red brick collage buildings, surrounded by greenbelts and miles of trails. It is worth the time.
From Boulder, start back on Hwy 36 to Rocky Mountain National Park. There are little towns on the way, tall trees leaning under weight of melting ice. It should take about two hours of drive to reach to the summit of Rocky Mountains. Another beautiful town of Estes Park awaits you there. If your schedule permits plan to stay over night. Nice little cottages, rivers and mountains. Lot of water activities.
Once in national park you may choose among couple of trails that may fit your taste for hiking. Other activities include camping, fishing, hiking, horseback riding, mountaineering, photography, winter sports activities etc.
Depending on weather you may find completely frozen lakes surrounded by mountains, all covered in snow. Kids as well as adults can even skate on the surface. After April when water starts melting you get to see beautiful, playful waterfalls.