Description: This is a photo I took inside of the Pantheon. You can see the open oculus above which lets light inside this ancient structure. The Oculus in the Pantheon has always been open to the weather, allowing rain to enter and fall to the floor, then it is carried away through drains. In the picture, sunlight streams through the opening and strikes the lower part of the dome. The bright opening and the surrounding smooth concrete above the coffering resembles an eye, giving the opening its name.