From Longman Dictionary of Contemporary Englishwindowlesswin‧dow‧less /ˈwɪndəʊləs $ -doʊ-/ adjective without any windows a windowless basement room
Examples from the Corpus
windowless• They reached the entrance to what was probably the least damaged of the buildings, long and windowless.• Within this room there was a second door, which led to a windowless cubicle that contained a toilet and a sink.• The camera settled across the street from a windowless exterior set in a row of shopfronts.• Another story she told was about a peasant who kept trying to bring daylight into his windowless hut in a bucket.• The wash-house sat between the stabling and a dark windowless place where coals and winter logs were stored.• It was a soundproof, windowless room at the end of the corridor on the second floor.• He stood up and pointed it at the far end of the barn where a target was tacked on a windowless wall. 