Fetching details from the dictionary...
cavern; grotto
「窟」 has another reading with different meanings.
嵐を避けて旅人は岩屋に身を寄せた。
To escape the storm, the travelers took shelter in the cavern.
岩屋の奥から清水が湧き出ていた。
Clear water was welling up from the depths of the cavern.
修行僧がこの岩屋で数年を過ごした。
An ascetic monk spent several years in this cavern.