Some things to remember, 100 years ago it probably was 6 miles away. More than likely, it is mentioned on some of the plat maps of the property. Those are usually available for viewing at the county court house. Copies usually are not too expensive, couple dollars a sheet. Use the info from the old plat maps, overlay to a current may or aerial photo and pinpoint better. One of the hardest things to make disappear is a hole. Remember the part about smoke visible several miles away? Almost all caves have more than one opening. If it was a 5 minute job to locate it, you could buy tickets and take a tour. A little leg work, a cover story, research paper for college? Checking accuracy of plat maps as perceived versus drawn? Use your imagination and do not give up so easy. It must be right in your back yard. During the winter, when there is a light covering of snow on the ground you would be amazed what snow or lack of, will show you about what is underground.
Talk to some of the oldest people you can find, they would love to visit with you! Have a few pictures of the terrain, an aerial photo or 2, the names of the landowners of record in the area, etc.
Keep at it, winter is not too far away and it would be a great research project for the when it is too cold outside to dig little holes.
Keep us posted.
GOOD LUCK!!!!
Bob