This is an universal project, which gives a fragment of sky to everyone whose life is spent inside the endless tunnels of subway. In modern cities human suffers from the lack of contact with daylight and a disorder of circadian rhythm due to it. The daytime passed in subway is critical on this issue, because in most large cities around the world, the average commuting time on the subway is more than two hours per day, while this period of time is the best for us to feel the time change in natural light. So here is a device that serve as an observation window of daylight on platforms of subway, it is universal for almost every platform with full-height screen door. It uses fiber optic to bring down the sunlight in real time, and project the light at the junction of platform and compartment, at the position of screen door so we can observe the sunlight each time when we are at a platform, whether we are in the carriage, getting on or off, or waiting. Observing the light, is to trace the time of the world and ourselves. The purpose of this project is to help people regain the lost autonomy of life, time and thoughts by getting daylight back to its place in our daily track.