And I found this
http://www.greatdreams.com/solar/black-sun.htm
Shambhala.
From some of the accounts available, Shambhala appears to have been a centre of spiritual enlightenment, very reminiscent of James Hilton's 'Shangri-La', but others say that it was a centre of occult power and arcane teaching. Its leader was thought variously to be either an evil, tyrannical Sorcerer-King or a God-like 'Lord of The World'. We seem to be left with a choice as to which story we prefer to follow, and evidently which Path one desires to follow, too. The evil Left, or the good Right!
Apparently there were two factions (as in Hyperborea), one of which followed the Golden Sun, and the other the Black Sun. (The 'Black Sun', incidentally, was as prominent an emblem of the Nazi mythos as was the Swastika!) According to Jean-Claude Frére, author of 'Nazisme et Sociétiés Secretès', the people of Hyperborea, after migrating to the Gobi Desert over 6000 years ago, founded a new centre, which they named Agartha. It became a great centre of world learning, and people flocked there from all over the world to enjoy its culture and civilization.
However, a huge catastrophe supervened, and the earth's surface was devastated, but the realm of Agartha somehow survived, under the earth. The legend continues to relate that, as with the original Hyperboreans, the Aryans now split into two factions: one group heading north-west, hoping to return to their lost Hyperborea, and the second going south, where they founded a new secret centre under the Himalayas.
Jean-Claude Frére concludes: The sons of the Outer Intelligences split into two groups, one following the 'Right Hand Path' under the 'Wheel of The Golden Sun', the other the 'Left Hand Path' under the 'Wheel of the Black Sun'. The first preserved the centre of Agartha, that undefined place of contemplation, of the Good, and of the Vril force. The second supposedly created a new place of initiation at Shambhala, the city of violence in command of the elements and human masses, hastening the arrival of the 'charnel-house of time.'
According to Peter Moon, in his book 'The Black Sun', the ultimate concept of Thule is well represented in the myth of it as the capital city or center of Hyperborea, a word which literally means 'beyond the poles'. As it is beyond the poles, Hyperborea is positioned as being outside of this dimension. Thule, being in the center, is positioned as the source of all life on Earth. In Greek mythology, Pythagoras was taught sacred geometry by Apollo, a god who was identified as a resident of Hyperborea. In Pythagorean teachings, the Earth itself geometrically unfolds from a void in the center.
This void has been recognized by many ancient groups, including the Sumerians, as the Black Sun. In this sense, Thule is synonymous with this Black Sun.