My belief is that the Grail is of a Divine/primordial/spiritual nature and represents the life that is in perfect harmony with God's will. The further away from God's will we stray, the less we perceive of the Grail and that's why I believe music is so important because through music we can perceive primordial life.
If we could transport ourselves to the next higher plane, we could probably be able to perceive the Grail as some kind of Jewel, a "Sun" and that "Sun" would represent the visible presence of the Divine Realm that, unfortunately, we cannot see from earth.
However, Revelation speaks of "New Jerusalem" and I wouldn't be surprised if this is the Grail or the Temple that houses the Grail.
If this is the case, then after Armageddon, the Grail or "New Jerusalem" will once again be visible from earth and everything on earth will swing in harmony with Creation. Earth will become a paradise and be a true reflection of heaven, as it should have been from the beginning.
So, the Grail to me is not only an obeject made of Divine energy but also a consciousness, a Christ consciousness.
This is my personal view of the Grail in a nutshell!
How do you see it Mark?