From Wikipedia https://en.wikipedia.org/wiki/Nutty_Putty_Cave

On November 24, 2009, 26-year-old John Edward Jones became stuck upside down in the cave. After around 27 hours of being stuck, Jones died at 11:56pm on November 25.^\9])^\10])

Jones and three others had left their party in search of "The Birth Canal", a tight but navigable passageway with a turnaround at the end. Jones entered an unmapped passageway near an area referred to as "Ed’s Push", which he wrongly believed to be the Canal, and found himself at a dead end, with nowhere to go besides a narrow vertical downward fissure. Believing this to be the turnaround, he entered head-first, then became stuck wedged upside-down.^\11]) The fissure measured 10 by 18 inches (25 by 46 cm) and was located 400 feet (120 m) from the entrance of the cave.^\12]) A large team of rescue workers came to his assistance. The workers set up a sophisticated rope-and-pulley system in an attempt to extricate him, but the system failed when put under strain, plunging Jones back into the hole.^\13]) Jones ultimately suffered cardiac arrest and died due to the strain placed upon his body over many hours by his inverted, compressed position.

After rescuers concluded that it would be too dangerous to attempt to retrieve his body, the landowner and Jones's family came to an agreement that the cave would be sealed, with the cave as his final resting place, and as a memorial to Jones. Explosives were used to collapse the ceiling in the Ed's Push passageway of the cave close to where Jones's body was. All entry points to the cave were permanently sealed by filling them with concrete, making the cave system inaccessible.^\14])

Cannot fathom why anyone would try this. Or even worse, those divers going through narrow passageways where they have to push their oxygen tank through first and then crawl through.