Abraham Lincoln probably took his first drink of water from Sinking Spring, and its dependable water source was undoubtedly an important factor in Thomas Lincoln’s decision to purchase Sinking Spring Farm. The spring is an example of a karst window, an unusual landform and a special type of sinkhole that gives a view into the karst aquifer. Typical of Kentucky’s karst topography and hydrologic systems, it is a significant natural resource whose water drains through the subsurface and empties into a branch of the Nolin River a short distance from the park. Sinking Spring is part of a network of springs and subsurface streams in and near the park, and it was also known as Cave Spring and Rocky Spring. Travelers often paused there to drink its refreshingly cool water.