I visited this place back in 1986 when Snail Shell Cave was only known to the locals. To get to this what me and my bud called the Gallery, we had to crawl through a tight gap. My bud went back a couple weeks later with his girlfriend at the time and snap pics inside the place because we didn't bring a camera - just batteries and flashlights. That's the extent of my spelunking career.
We first heard about the place from some local that visited the Shoney's restaurant to frequented on Nolensville Rd at the corner of Old Hickory Blvd. He gave us basic directions, so we headed out the next day to check it out. After parking, we had to hike in to see the following:
In our eyes it was beautiful and couldn't wait to walk down to the entrance of the cave. Once down there, we learnt that there were two entrances, one of which (on the left) would require a boat to traverse. Written above on stone above the cave entrance was something about a drowning including the date of the event. We decided to come back and see how far we can go in the other entrance. A couple weeks later we returned and went in about 3/4 mile. Save Googling to confirm, the consensus is that there's over 7 miles of passages, some of which have yet been explored. It's told that it could rain 20 miles away and the next day the caves would flood, hence the drownings. Five count, taxing my memory of what was scribed.