Here are some of the greatest Unsolved Mysteries of all time. (5,4,2 are described as a whole and a specific)

#5 - The Underground Mystery 0:53
#4 - Unexplored Caves China 4:17
#3 - How the Moon was Formed? 5:35
#2 - Undiscovered Civilization 7:51
#1 - Gravity 9:03

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