Real Life Hiker Disappearance
I saw this movie not long after reading online about a hiker called Kenny Veech.
Apparently, he found a weird cave on one of his hikes in the Nevada desert. He said it was near some government base, and that the cave entrance was M-shaped. Veech experienced odd vibrations in his body the closer he got yo the cave. So he got spooked and left. He stated later in a YouTube comment that he was going back to try to find the cave again and this time to go in.
He went back with a video cam and gear, but didn't find it. Then he went back again and went missing. They found his cell phone by an old mine shaft, but no trace of him.
Anyway, as I watched this movie it made me think of that account.