subterranean

• The entrance to this house is subterranean, and consists of one or more galleries debouching under the water. —  The Hunters' Feast Conversations Around the Camp Fire
• On the first voyage it would have been easy to persuade oneself that the river was soon to become subterranean, but the Major having solved the enigma, we could look with indifference on the threatening prospect. —  A Canyon Voyage The Narrative of the Second Powell Expedition down the Green-Colorado River from Wyoming, and the Explorations on Land, in the Years 1871 and 1872
• There is no trap door leading into either subterranean or overhead apartments. —  The Master-Knot of Human Fate
• Listen The man's faculties must have been keyed up to the pitch of his nerves, for to me the night remained as voiceless as a subterranean cavern. —  The Best Short Stories of 1915 And the Yearbook of the American Short Story
• The unhappy passion which he could at times smother, but never subdue, went boring away into his heart like a subterranean fire, consuming his vitals, and occasionally breaking forth into a wild blaze. —  Essays on Scandinavian Literature

Roget's II: The New Thesaurus

Used in the Same Context