Which US state has the longest cave system in the world?

went to mammoth with the family in 2019, it was really cool and we just saw a small section of it. worth a look.

tunegrabber, been there a couple if times, as well as other famous caves. However, a cave system that was being mapped by a group of spelunking, including my x, was the coolest experience of all.

Those runoff rivers from the Appalachians.