The national monuments have recently become a really big interest of mine. They offer a much smaller scale look at the National Park System and they are just fun to visit by yourself or with your family.
During a recent trip to Colorado, I ventured out to the Florissant Fossil Beds. Although a small monument, it offered a surreal experience. I went right after a snowfall occurred and the ground was neatly covered in powder.
Seeing some of the petrified redwoods surrounded by snow was magnificent.