Sri Aurobindo
Letters of Sri Aurobindo
Volume III - Part 2
You had asked the other day about the subconscient, what it was. In the vision you describe you were shown the universal 
subconscient in the figure of Patala, a place without light of consciousness and, because universal, therefore without bounds or end – the dark unconscious infinite out of which this material universe has arisen – it is walled with darkness on all sides, it seems also to have no bottom. The Light comes from above from the higher consciousness and coming down through the mind and heart and vital and physical has to pour down into this subconscient and make it luminous.