After leaving the East Portal, a tunnel leads to the Crater's Eye, a kiva-shaped skyspace located in the center of the caldera (volcanic basin). Exiting from another tunnel one can walk into the caldera known as the Plaza. Surrounding the crater's eye are four limestone plinths aligned to the cardinal directions, upon which one lies to view the celestial vaulting of the sky. The experience of celestial vaulting has been enhanced by shaping the crater. James Turrell is one of the most celebrated American artists working today. Born in California in 1943, he grew up with an enduring love of aviation and the sky, as well as a fascination with light. His Quaker background also substantially formed his approach to life and art, with its emphasis on silent access to the "light within." From age six, Turrell was urged by his grandmother to "go inside and greet the light" at Quaker meetings. In the early 1960's, Turrell studied perceptual psychology at Pomona College, taking additional classes in other scientific disciplines, such as mathematics, geology and astronomy.