Conrad,
There were copper mines on the property in colonial times. I've heard that when some of the older buildings were removed years ago, remnants of the mine tunnels were found underneath some of them. There's also a water filtration tunnel on the property, that Johnson & Johnson had built about 100 years ago to provide water from the Raritan River for cotton manufacturing. The water was purified in an on-site water filtration system. That water tunnel still exists, too.
Margaret