nether regions

plural of nether region

Hell; a realm beneath the surface of the earth conceived as the abode of the souls of the dead and, sometimes, as the abode of demons or evil spirits.
(broadly) A place which is subterranean or enclosed beneath a surface, especially one which is dark, dank, or otherwise inhospitable.
(euphemistic, humorous, sometimes) The private parts between the legs; the groin or buttocks.