What is Lindsey's secret refuge in the novel, An Abundance of Katherines?

Lindsey has a secret cave on some of the land that Hollis owns. Lindsey keeps some pillows, a sleeping bag, flashlight and a jar of moonshine in the cave. The cave is a secret refuge for Lindsey that nobody knows about. The only person Lindsey tells about the cave and the only person she takes there is Colin Singleton.