Impatiently he cleared the other two shelves of all they held (mainly old clothes and shoes), removed them as he had done with the middle one, and unlocked the sliding door at the back of the closet. The elephants were forgotten, he stood on the threshold of a secret passage. Its deep darkness was total but something about its speluncar acoustics fortold, clearing its throat hollowly, great things, and he hurried to his own quarters to fetch a couple of flashlights and a pedometer.
page 125 Pale Fire by Vladmir Nabokov
then to the dictionary for the word “speluncar”. a., speluncean a. pertaining to or like a cave.