Translation:At the left side of the building, go down.
Alrighty having discussed this with indonesian hubby. You need to say "turun ke bawah" to mean go down (even though "turun" means down anyway). The same for "naik ke atas" is used when you want someone to "go up" (upstairs etc). You can't use just "turun" or "naik" on it's own for this example.
Yes, that's right.
This verb is almost always used in combination with another word indicating the location.
'turun ke ...' = 'going down to ...'
'turun dari ...' = 'going down from ...'
In this sentence it would be strange to omit the word 'bawah' (...) (the location).
@Rick392366 is correct. When using "ke" it is used in place of "to" in the English Language, but only when indicating a location. i.e. "Going to Church." is "Pergi ke Gereja."
Shouldn't the English sentence have something more to explain "bawah" like "go down to the lower floor"