noun
deep mountain valleys
A yojijukugo (four-character compound) used in literary or descriptive contexts to evoke remote, secluded mountain scenery.
深山幽谷を分け入って、ようやく隠れ里にたどり着いた。
We pushed through deep mountain valleys and finally reached the hidden village.
A yojijukugo combining 深山 (deep mountains) and 幽谷 (secluded valleys). The exact historical origin is uncertain, but it follows a common pattern of pairing two two-character words to create a vivid literary image.