Hit the slopes.
Whether you and your significant other are advanced skiers, or whether you're more of a bunny trail kind of couple, Colorado is famous for its fantastic skiing and ski resorts. The most famous skiing is in Aspen, although Vail is also known for its gentler slopes. Most ski resort towns also offer features such as great restaurants and quaint shopping. Many hotels, bed and breakfasts and resort locations offer romantic features like scenic views of the mountains, hot tubs and fireplaces.
Take a hike.
Colorado is home to many beautiful hiking trails in its mountains, if that is your idea of romance. In Georgetown, Colorado there is Mount Bierstadt which overlooks the famous lake The Abyss, as well as Mount Evans. In Rocky Mountain National Park there are also many scenic hiking trails for all kinds of skill levels overlooking beautiful natural features such as Gem Lake. Near Vail there is Wilder Gulch whose meadows are full of wildflowers in spring and summer. Here there is the option to take an easy walk through the meadow or continue on a trail up Ptarmigan Pass.
Besides hiking, and during the months when there isn't any skiing, Colorado still has lots to do in the great outdoors. Some recreational areas offer horseback riding and biking, while golf and tennis is available in many areas as well. Recreational boating, white water rafting and canoeing can be found in many of Colorado's rivers and lakes. If staying at a resort, you'll find that many of these options are available on site or will offer transportation services to get you where you want to go.
Relax in a hot spring.
Colorado has many geothermal hot springs. Some are located in remote locations, while others are easily accessible. Some of the most popular springs are Glenwood Springs, Steamboat Springs, Pagosa Springs, Ouray and Hot Sulfur Springs. Many of the hot springs locations offer spa and sauna services and some are even clothing optional.