In front of the papal altar is the confessio that marks the grave of St. Peter, and right above is where the dome is located. impressive colorful vaulting with sixteen ribs that are supported by four massive pillars. The dome has an ogival shape, or more slender upward with a double shell structure which stands on a base distinguished into three parts. These three parts each have a set the eight buttresses at the drum, which made up of double columns that frame windows. The dome has protobarocche forms that allow light come through into the space between the two shells. Within the lantern there is a painting of God the Father, which to the pagan represents the eye of god looking down on his sons and daughters.
VR Tour: http://www.vatican.va/various/basiliche/san_pietro/vr_tour/Media/VR/St_Peter_Altar/index.html