This is the 588th most frequent Serbian word.
истоку
"Истоку" means "to the east" in English.
In this sentence, 'истоку' is used as a noun in the dative case to indicate the location where the Sun rises.
Сунце излази на истоку.
The Sun rises in the East.
Here, 'истоку' is applied as a noun in the dative case to denote the direction of movement.
Путовали су ка истоку целу ноћ.
They traveled eastward all night.
In this context, 'истоку' serves as a noun in the dative case, describing the orientation of the building.