terra incognita

tuntematon maa, terra incognita land Land that has never been explored or mapped; chart uncharted territory.
By extension, ideas or concepts that have not yet been tried or explored.
2009, Gary Clark, Quadrant, November 2009, No. 461 (Volume LIII, Number 11), Quadrant Magazine Limited, page 9:

The concept of the unconscious or an inner terra incognita, an unknown country of the psyche that precedes and predicates the Cartesian subject, the focal point of rational consciousness, was a revolutionary idea.