I think the excerpt you are talking about is...
"Dantès entered the second grotto. The second grotto was lower and more gloomy than the first; the air that could only enter by the newly formed opening had the mephitic smell Dantès was surprised not to find in the outer cavern. He waited in order to allow pure air to displace the foul atmosphere, and then went on." from The Court of Monte Cristo.
A synonym or the word grotto could be cave/cavern. Hope this helps!
