In the recent case of the Thai football team that got trapped in a cavenin Chiang Mai, the best thing they could have found were the rescuers!
However, wouldnt it be exciting to find some hidden treasure left behind by a pirate from years ago, or a message in a bottle sent from half way around the world!
What youre most likely to find however, are bats and a load of super bacteria.
It could be worse though. You kight find Elon Musk and his mini submarine!