Unthanks Cave Natural Area Preserve is a 171-acre protected area in Lee County, Virginia, created to safeguard the only known entrance to Unthanks Cave, a biologically rich cave system extending about seven miles. Its streams drain a significant karst area south of the Powell River and support unusual invertebrate life, including the rare hydrobiid snail Holsingeria unthanksensis, first discovered there in 1986, along with other notable cave species. The Nature Conservancy bought the entrance in 1987 as its first cave system purchase in Virginia, and the property passed to the Virginia Department of Conservation and Recreation in 2004. The cave is now gated and reserved for scientific access.