Small Crack Turns Into A WIDE Mine Shaft

This adit was the widest mine I have seen, Probably 50 foot across. Most of it is flooded. It looked like running water in it but it might have been a draft creating waves on the surface coming from another entrance. update: we figured out where this one goes. https://www.youtube.com/watch?v=TFG7l-x60GQ&t=229s
we point it out towards the end of the video it's the adit coming in from the right.