I was eighteen. My friend and I were driving around our town's massive nature park at night, maybe around 11:30-Midnight-- I can't remember for certain. We were coming up on a cliff colloquially known as Lover's Leap. As we approached it, we saw a girl standing at the edge of the cliff.
We got out to see if she was okay-- we didn't suspect that she was a ghost or anything weird until later, because she looked as solid and real and tangible as any other person. The only weird things that we noticed at the time was that she was wearing a torn, strapless summer dress and no shoes in the dead of winter, and that she looked absolutely terrified out of her mind.
When we drove up, she was looking around frantically, as if she was afraid someone was going to jump out of the trees at any moment. When we got out and asked if she was okay, her head whipped around in our direction, and she asked if we could help her.
Walking back to the car, I turned to my friend to tell her to unlock it so I could get out my phone and call the police. I waited with my hand on the door handle while my friend fumbled hurriedly with her keys.
When I'd gotten my cell, I looked up to ask the girl where she lived, but she was gone. Neither my friend nor I had heard any rustling in the trees that would suggest that she ran back through them, and, panicking, we rushed to the edge of the cliff, fearing that the girl had jumped or fallen in her panic.
We looked over the edge, shining my phone's flashlight into the darkness, but there were only rocks. The girl had disappeared completely.
Needless to say, we straight booked it back to the car and got out of dodge as fast as we could.