I think "Mount Sumeru/Meru" may have been once understood as an intangible nexus connecting unseen realms to the material world. I think that some ancient śramaṇas, shamans, and meditators in cultures with the concept of an ethereal world axis may have entered heightened states of consciousness and then followed this axis into what they perceived as other planes of existence. In this sense it may have been understood as something like the main road into unseen worlds of samsara, found only with the mind. I think that there is some evidence suggestive of this possibility.
First, there are the many hints that Mt. Sumeru was not viewed as an actual mountain. For example, it was thought to be higher than any actual mountain. It could be portrayed as a pillar or a post. It could be depicted as penetrating the spiritual universe "from top to bottom." (See Buddhist Cosmology by Akira Sadakata. On the other hand, the name of the "mountain" may have been derived from the sacred Persian mountain Merv.)
Second, there are similar concepts in other ancient cultures. When I used to study ancient Norse religion, I remember reading that a scholar suggested that the Norse shamans might have used the "world axis," conceived as the mighty tree Yggdrasil ("The Steed of Ygg") in the center of the world disk, connecting all spiritual realms to the material one, to visit unseen worlds inhabited by gods, spirits, and the like. Perhaps there is also a connection to "Jacob's ladder."
It's just an idea. If it is correct, however, it suggests that ancient people in different parts of the world may have used a similar "map" to approach "unseen realms."
I should dispel the suffering of others because it is suffering like my own suffering. I should help others too because of their nature as beings, which is like my own being. When happiness is liked by me and others equally, what is so special about me that I strive after happiness only for myself? When fear and suffering are disliked by me and others equally, what is so special about me that I protect myself and not the other? Shantideva, Bodhi[sattva]caryavatara 8.94-96