The reason the holy mountain is invisible is because it is esoteric [1]. It derives its existence not from being a pile of material rock that anybody could see if they looked at the right place, but from being a collection of immaterial experiences that can only be perceived by souls that are in the right state of consciousness. It is invisible, in other words, not because nobody can see it, but because only some people can see only a part of it.
[1]Literally, of or pertaining to the self.
There are enough people seeing enough parts of it that one can conclude with confidence, without directly experiencing it oneself, that it does exist. As always, the proof of the pudding is in the eating. Everything you hear about The Holy Mountain should be taken with an appropriate amount of salt [2] until you witness it for yourself.
[2]In this perspective, my job here isn't to show it to you, rather to decrease your sodium intake until you find information about it palatable. Whoever designed the Holy Mountain definitely has a brilliant sense of humor; if you don't think it's real, that belief by itself will prevent you from seeing it. Close-minded skeptics automatically exclude themselves from being capable of receiving the sort of evidence that might change their mind [2-1].
[2-1]And honestly, even when they are presented with strong evidence, there is a whole host of rationalizations that can be used to deny shockingly intimate experiences.
The perspective that I've found useful is to treat the Mountain's visibility as a function of how far up it one is; you can only see the portion that lies beneath you. Since almost everyone starts their life at the very bottom in the foothills, and since most people do not invest a lot of effort in trying to climb it [3], it remains almost wholly invisible to the vast majority of people.
[3]Climbing the mountain, moreover, is not a linear experience. It takes a lot of time and effort before one feels like one's making progress, and so this leads many people to give up after they've barely started.
Let's suppose you're on the foothills, and you're curious to know where to find it, if for no other reason than I'm telling you it's there, and I've got your attention. I'll start by sharing how I found it: the jigsaw puzzle →.