According to the Bard Llywelyn Sion, every human must begin in Annwn, know and suffer everything in Abred, before entering the Great World of Gwynvyd.* The Celtic mystics of Wales wrote that a person ascended to Gwynvyd if their life had shown a predominance of good over evil, understanding without doubting, and no fear of death.
In the underworld all change must begin before the changes begin to occur in the middleworld. Just as every thought begins in the subconscious before it can become a living reality in the outer world of manifestation (i.e. thoughts are things). All creation must first take place in the upperworld or underworld before they can take place in the middleworld, or where we dwell in our realities.
Set up your sacred space as usual, casting your protective circle. Put on your drumming tape, relax your mind & body, then do your "Inner Tree Meditation". Step out of your body then climb up the world tree to the upperworld.
When you reach the edge of the doorway, stop a moment to adjust to the sunlight, and to wait for your spirit guide to aid you. This is the realm of the Goddesses and Gods known throughout time. You may or may not only encounter Celtic deities, but others as well.
The center of the upperworld holds the Sacred Chalice on the altar. The Chalice symbolizes undergoing a spiritual initiation. You may be denied the right to partake of this initiation if you are not ready for it. Any creature or symbol that you see three or more times is important, as it is a message being sent to you.