The region of Cappadocia is located in the middle of a once-active volcanic area of central Anatolia, presents a spectacular landscape created by characteristic geology and architectural patterns that have been generated by relation with humans and nature. The impact of arid climate, material, topography, and defensive requirements were the factors in vernacular architecture. The soft material allowed carving to the rock masses for the structure of the spaces. The underground settlements were created through time due to provide safety against attacks and It was placed in it both the living area and warehouse, educational, religious, wells, ventilation systems, or stables for animals each other by tunnels. The deepest Underground city is Derinkuyu which reaches 90m below equipped with 52 ventilation tubes 80m height. Climate controlled but without natural light. The idea is creating daylight in the Derinkuyu Underground settlement in Cappadocia. The fenestral lens collects sun rays transmit to the optical fiber cables and cables transmit the light in a deep underground. Thus, Illumination generates connections between outside and underground. A part of the fiber cables links to the circle light distribution system which is placed interior of the space. Illumination in the cave creates a spatial connection between the outside and the underground it directly reflects the fluctuation of illuminance in the day.