I live in a very old town and out northeast is a dam that used to be part of the underground railroad and has a sordid history, including deaths of locals over the years, multiple instances of drowning. Overlooking the dam is a steep bridge that has railroad tracks on it and a steep ravine on the southern side with no access. One night, a friend and I visited late at night during late summer of 2009. It was a very dark night other than the moon, which helped us navigate up the back and to the railroad tracks overlooking the dam. We sit on the tracks, facing the steep ravine, and I pick up a few rocks and throw them over, and you'd hear them crash. Suddenly, a rock was thrown back. The moon had lit the entire area and from where we were sitting, we could see the ravine. Nobody was down there. So I threw a rock, and again another was thrown back. This went on for a couple more minutes before my friend and I decided we'd had enough and it was time to leave.
I have other stories about this place too.
TL;DR threw rocks with a ghost friend