There was also an immense cave recently discovered here in Tennessee called Rumbling Falls. You have to rappel into the main chamber from the center of the roof which is over 200ft high. I talked to someone that has been in it and they described it as like being in outer space. The walls are too far away for your lights to reflect off of so you are sliding down a rope in pitch blackness for what seems like forever!
Perhaps the Social Security lock box will be located.