To be spiritual means to somehow transcend the physical. In terms of our experience, “physical” fundamentally means the body. The most intimate physicality in existence for you is your body; and this body is just a piece of earth. So, one instrument or method for a person to transcend the physical is to constantly remind the physical – experientially, not intellectually – of what it really is. The physical body has a lot of fancy ideas about itself, so we always want to keep it close to the earth to remind it that it is just a piece of earth. You are just a small outcrop of this earth, nothing more nothing less. Right now you are an outcrop who prances around, after sometime you will become a small mound. Just sitting down cross-legged on the floor experientially reminds the body of this in some way because the moment the body is in touch with the earth, it knows it is earth.
This reminder must be on all the time. In a mountain, this reminder is happening in a very big way. A mountain is a place where earth has risen to reach out to you. If you make a hole in it or go into a cave, earth is on all sides; it is a big reminder. That is why, though the conditions are not comfortable, all spiritual beings generally move to the mountains. Mean sea level would be much more comfortable because you could live there with the bare minimum. On the mountains, it is very difficult. But still they choose mountains because it gives you a closer contact with the earth. It is a constant reminder for the body, that the play of elements in the earth and the play of elements in this body are not different.