19. Haunted Parks: Mammoth Cave National Park, Kentucky

Mammoth Cave is the largest known cave system in the world. Artifacts found inside the cave suggest people have been exploring Mammoth for thousands of years, and yet scientists are still discovering new passageways and underground rooms. It has served many purposes over the years including being a saltpeter mine, a tuberculosis clinic, and private theme park. Visitors often report seeing apparitions and hearing things. There’s nothing spookier than being in a huge cave system with lingering spirits. 

Sources:
https://en.wikipedia.org/wiki/Mammoth_Cave_National_Park
https://npshistory.com/morningreport/incidents/maca.htm
https://www.nps.gov/articles/000/tragedy-at-sand-cave.htm
https://listverse.com/2023/04/21/10-people-who-went-missing-in-mammoth-cave-national-park/
https://www.nps.gov/parkhistory/online_books/regional_review/vol3-4-5h.htm
https://www.nps.gov/maca/planyourvisit/other-cave-tours.htm
https://www.outsideonline.com/adventure-travel/national-parks/national-parks-ghost-stories/
https://www.nationalparkstraveler.org/2009/10/mammoth-cave-national-park-harbors-more-few-ghost-stories4820