The mountain god is the traditional Korean religion. So when accepting Buddhism, at least they had to tend to respect local traditional religion. As a result of those history, there are the place for the mountain god in each temples.
The mountain god was the one among the the 3 Holy Divines.
So if there is 3 holy divines shrine, there is no need to build mountain god shrine in same temple.
Actually the mountain god was believed as the protector of the temple.
It was so strange that there were 2 shrines serving for the mountain god in one temple.
The style was quite different each other between 2 shrines.
The mountain god shrine was quite different from the 3 holy divine shrine.
The mountain god in this temple seemed the attached building of the large buddhist hall.
It had an independent style, but this shrine was linked through the corridor with the main hall.
The mountain god shrine was small though, it had the entire elements as the buddhist building.
The 3 Holy divines shrine had an ordinary style of the building like that of other temples.
One thing unique is it has its own wall.
The building in this temple having its own wall is the most characteristic thing in this temple.
It could be supposed that the concept of the space in this temple must be different from others'
Anyway, why did they build 2 same meaningful shrines in one temple ?