John Ackerman has spent millions procuring a majority of the known caves in Minnesota, which add up to dozens of miles of underground passageways and likely make him the largest cave owner in the U.S. He collects and charts them in the name of preservation, but his controversial methods have created many opponents.


https://www.outsideonline.com/2414888/john-ackerman-caves-minnesota?fbclid=IwAR2js8B_VNPi4-OlOXdASPmhUZdQfVA-_XZUefZfO8ViOuftpaC4q9fBP4M#close

Also here: https://ukcaving.com/board/index.php?topic=26629.0