rock door; stone door to a cave
Refers to a door made of rock, especially one sealing a cave. Most famously associated with the myth of Amaterasu hiding in the heavenly rock cave (天の岩戸).
The myth of the heavenly rock door is famous even among Japanese myths.
A large rock door was fitted at the entrance of the cave.
Compound of 岩 (iwa, 'rock') and 戸 (to, 'door'). The reading is a straightforward combination of the two elements.