deep in the forest; heart of the forest
Refers to the interior or depths of a forest, often with a sense of remoteness or mystery.
森の奥で小さな小屋を見つけた。
I found a small hut deep in the forest.
森の奥から鳥の声が聞こえる。
I can hear birds singing from deep within the forest.
Compound of 森 (もり, 'forest') + の (possessive particle) + 奥 (おく, 'interior, depths').