Concentrated urbanization is a notable feature of land use in Korea, where approximately 75 percent of the land area is mountainous and thus, it becomes more important to utilize urban space effectively. For the great cities of our present time, thus, the use of underground space has become a necessity and a major producer of an underground amenity, energy saver and economy. One of the problem in underground environment stems from the fact that most of us still has a great longing for nature sunlight and unobstructed view to outdoors. In this paper, we will focus on the contribution of sunken structure in the underground spaces as a potential daylighting resource. When daylight is introduced into a space through the sunken, its role in general illumination is what is of interest in this study. To achieve this goal, a serious of computer simulation of sunken configurations in underground space has been performed. Result reveals that the daylighting potential of the sunken structures may help the general illumination in some level of significance.