This looks like the opening to a cave carved out of a ragged, stone cliff. It's actually the bottom of an enormous and obviously ancient Douglas Fir. I'd need my fisheye to take in the entire base, because it's growing right next to a cliff and I can't back up far enough to get a full view of it, even with my 12mm lens. Notice the circular growth on the upper right of this image. I show it head on in the next image.