The "tunnels" at Batsto probably aren't as exciting as it sounds. I think there are three, only one though can you walk down. One is kind of like a chute that is underneath the dining room area and goes under the basement floor. From what I remember someone might be able to crawl through it, but no thanks. I was told it could have been used for storing coal, I don't really know for sure what it was used for. The other was underneath the floor to the far right of the mansion, right across from the ice house. There is a small kitchen there were the workers hang out. We discovered that part of the rug pulled up and under it was a "trap door" of sorts. We pulled up on the door and discovered what looked like a small trench. I was told the state had discovered it years ago and dug it up and thought was where the people of the mansion once threw away their trash or simply buried it. A lot of chicken bones were in there. The last "tunnel" is located underneath the kitchen. In the basement there is a large fireplace used for cooking and to the right of it someone dug a small tunnel. I think it makes a right and then heads towards the front of the mansion. You can actually walk into that one, but I forget how far it goes, 20 or 30 feet? It just dead ends. Maybe it was used for storing things a long time ago. I'm pretty sure I have read about and even seen drawings of the "tunnels" at Batsto in a book, but I can't remember which book it was.
I know it's not that exciting, but it is interesting and would love to know why someone put forth all that effort to create them.