It was a huge spirit cave covering several acres of area and plunging ten thousand miles deep into the ground, a place where nine underground energy veins met. Copious amount of energy would come rolling and rocking up from those energy veins, gathered by a 'Ninesky Immortal Aura Condensing Formation', which would also purify and compress them. They would finally go through a silver pearl the size of a human head placed in the center of the formation, transformed into the purest immortal aura.