An Abundance of Katherines
Everyone has a sanctuary away from the world, a place they go to when they've had a rough day or just want to be alone. For most of us it's our bedrooms, but for Lindsey it's a top-secret cave in the middle of the forest. The first time she tells Colin about it, she describes it as "my secret hideout. My super, incredibly top secret location that no one on earth knows about" (13.88).
Until now. She tells Colin about the hideaway and takes him there, even though her boyfriend TOC doesn't know about it. Her cave is her place to be by herself, which is especially important because she changes her personality depending on whomever she's with. The cave is the one place she can just be completely herself.
The cave doesn't just symbolize privacy and authenticity, though. Nope—Lindsey's cave is a big old symbol for s-e-x. Think about it: the cave is private, and no one is allowed to go there without Lindsey's say so; it's also where Lindsey bares all to Colin—at least metaphorically—telling him her secrets and things she's never told anyone else. Not convinced? Just picture a cave in all of it's dank, dark, hole awesomeness, and then remember that Lindsey invited Colin to come inside.