"Big Bertha", a massive 5-story tunnel digger has been blocked by a mysterious object. No one knows what the object could be. Some believe it is a massive boulder while other suggest it may be something a bit more interesting. Some even speculate it could be anything from a buried crashed UFO to a part of an unknown ancient civilization. The video below shows many news segments concerning the subject. I don't agree with everything the uploader put into the video but it's a good video no less.
If you are looking for a wild theory to get behind, perhaps it is the Sheti?