Yes, I have heard about it a lot and done some research on my own. I have heard of reports of flying objects coming out of craters in the north pole and they suspect that, that might be the connection between the world below and ours.
Of course, non of this has been confirmed and these days, there are so many theories about so many things one doesn't know what to believe anymore. My mind boggles sometimes when I read the things I do!
Of course! it boggles my mind as well. Out of the several "existence" theories, it is one of the more interesting ones!