Refers to a natural underground hollow, often with rocky walls; somewhat literary or formal compared to 洞窟 (どうくつ).
The island has several caves facing the sea.
The expedition team discovered ancient wall paintings inside a deep cavern.
Standard kanji spelling; 岩 means 'rock' and 窟 means 'cavern'.
Variant using 巌 (rocky crag); less common than 岩窟.
Compound of 岩 (rock) and 窟 (cavern). The exact historical derivation is uncertain, but the spelling is conventionally associated with a rocky cave.