You're going to need to pass a killer job application to see Arizona artist James Turrell's longest-running project. Turrell is an internationally acclaimed artist who works with natural and man-made light and environments to create ever-changing installations. His pieces have been featured in museums around the world, and since the '70s, he's been working on his biggest installation — inside an extinct, 400,000-year-old volcanic crater in northern Arizona.But don't expect to ever see it.Turrell doesn't give public tours and has taken very few private guests into the evolving space to experience what he calls a "celestial vaulting." Because of the angles of the crater and the space Turrell has created, a viewer looking up sees the sky as a dome instead of a flat horizon, creating the feeling of being "on the edge of the Earth."Phases of construction have been ongoing since the '70s, but more than 1.3 million cubic yards of earth have been moved to shape the crater bowl, and construction continues in various tunnels and smaller spaces that utilize its natural angles and reflective surfaces to play with the light that trickles in. Don't bother trying to find it or access the entrance — the natural observatory is remote and very secure. Rumor has it, Turrell's looking for an administrative assistant for the project, but like we said, you're going to have to pass a few tests (and take a number in what's likely to be a long line of Turrell fans and artists) before you gain access.