My take on it:
I think these energy or electro magnetic fields mess with the pineal gland somehow. The pineal gland (3rd eye) releases DMT, a psychedelic substance
responsible for making us dream. Many people who take DMT see the infamous grey aliens and describe what seems like an abduction experience.
Furthermore while on DMT time seems to stop. A minute looks like a lifetime but when the journey ends most people don't remember a single thing or
forget everything minutes later.
Now, two of my uncles had some hallucinogenic experiences because of depressions. One was missing for 2 weeks. I'll tell you, it's scary, in his
mind my father had died and my mother was talking to him by telepathy for the entire 2 weeks. Imagine his face when he saw my father alive in front of
him and my mother telling him she doesn't even believe in telepathy crap. lol he couldn't believe it. he was so sure. The other one talked to an UFO
who said to meet him in Azores islands.

Needless to say there was no UFO there... and both my uncles are over 40 and don't even believe in
these things.
All these experiences are related to DMT and brain malfunctioning.
So, my take on "the mystery mountain" is that there is some kind of earth electromagnetic field that totally disrupts our brain neurotransmitters
(remember, our brain is electrical). Probably some explorers trip so bad that they slip and die inside the caves. Others just leave and go wondering
about God knows where until the brain short circuits again and they return to normal. They wont remember the lost time because that is the primary
side effect of a heavy DMT experience.
I truly find this normal because I also had my share of Psychedelic Trance parties and I'm used to being around trippy hippies. I believe I saw
everything already =)
Anyway, research a bit the pineal gland and DMT.