secret, furtive, concealed; see hidden 2.
subsurface, sunk, sunken, subterraneous; see underground.
"subterranean." YourDictionary, n.d. Web. 22 June 2018. <http://thesaurus.yourdictionary.com/subterranean>.
subterranean. (n.d.). Retrieved June 22nd, 2018, from http://thesaurus.yourdictionary.com/subterranean
Located or operating beneath the earth's surface:
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