noun, noun which may take the genitive case particle 'no'
in the mountains; within temple grounds
Refers to being inside a mountainous area or within the precincts of a temple. The temple sense is less common and context-dependent.
There is still snow in the mountains.
The temple grounds are very quiet.
Many monks live within the precincts of this temple.
The young monks continue their strict training within the temple grounds.
境内 specifically means the precincts of a shrine or temple, whereas 山内 more broadly covers mountainous areas and only sometimes refers to temple grounds.
Compound of 山 (mountain) and 内 (inside). The temple-grounds meaning likely derives from the historical location of temples in mountainous areas.