Ben McDaniel
https://en.wikipedia.org/wiki/Disappearance_of_Ben_McDaniel
https://coolinterestingstuff.com/the-unexplained-disappearance-of-ben-mcdaniel

Naomi Uemura
https://en.wikipedia.org/wiki/Naomi_Uemura

Ludwig Leichardt
https://www.theguardian.com/science/2013/may/31/what-really-happened-ludwig-leichhardt
https://mysteriousuniverse.org/2015/11/the-mysterious-lost-expedition-of-dr-leichhardt/

Jeffrey Bush
http://uk.businessinsider.com/how-sinkholes-form-2015-1
https://abcnews.go.com/US/massive-sinkhole-swallowed-florida-man-reopens-years/story?id=33181156
The Unknown Tourist
https://www.prairieghosts.com/mammoth.html

Catacomb Explorer
https://www.youtube.com/watch?v=yxJkMlqYrys
http://www.the13thfloor.tv/2016/12/19/the-creepy-story-behind-the-infamous-lost-in-the-catacombs-video/

Luis Hernandez
https://en.wikipedia.org/wiki/Crandall_Canyon_Mine#Initial_collapse

Brian Kerr
https://ukcaving.com/board/index.php?topic=18983.0
https://www.yorkshirepost.co.uk/news/tranquillity-returns-to-site-that-claimed-a-young-boy-s-life-1-2590339

The Hannibal Boys
https://www.whig.com/20180322/whats-the-truth-behind-the-boys-who-vanished-in-hannibal#//
http://www.hannibal.net/news/20170510/mystery-over-disappearing-boys-remains-unsolved-50-years-later
http://charleyproject.org/case/joel-hoag

Kenny Veach
https://www.reddit.com/r/UnresolvedMysteries/comments/5qcwr3/what_happened_to_kenny_veach/
https://www.strangeoutdoors.com/mysterious-stories-blog/2017/10/25/kenneth-lee-veach-and-the-mystery-of-the-m-cave-strange-disappearances-from-us-deserts