It is a common saying that if you wish to hide something of great value, you should leave it out in the open. Such it is with the Holy Grail, which has been a great unsolved mystery for 800 years. However, nothing short of divine providence has willed it to be in the open for all to see as an astronomically large Signpost of God. The thesis of this book is that the Grail is related to an astronomical phenomenon mystically connected to the genesis of life on Earth - and for this reason it is called Holy.