Devils Den Nature Preserve, Fancy Gap, VA (1.9 mile loop, 321’ elevation). The name “Devil’s Den” refers to a 600-million-year-old cave formation comprised of several layers of rock, which contain many large rooms. A steep and narrow trail leads you through the wildflowers to this huge, spectacular cave. It rained last night and the rocks were slick. We’re planning to come back and explore further, we could see other rocks lower down and through the forest. A lovely yellow lab from a nearby house joined us for the entire hike.