James Turrell has created over 82 “skyspaces” like Three Gems in the world.   

Each skyspace is a room with a hole in it, through which you see the sky!  No, I don’t mean a window...Many of these super-minimal spaces include LED lights and unique architecture to make viewing the sky, which we do daily, a totally new experience.

Three Gems was commissioned by the de Young Museum in San Francisco in 2005, and you can visit it for free in the sculpture garden. This is the first skyspace he's done that's shaped like a dome. To check it out, you walk down a sloped path that cuts into the earth, which looks like it ends at a cement wall.

However, as you get closer you realize the path curves around the obstruction, which is not a wall but a big, rounded dome.  You enter the dome from a doorway on the back and find yourself in a circular room that could hold about 15 people.

Sit down on the bench around the edge of the room, and gaze upward at the smooth, curved ceiling that ends in a gaping circular hole through which the sun shines.  Or, since it’s San Francisco, where the gray, flat fog sits.  It’s easy to be mesmerized, and even disoriented by the stunning circle of light, and to forget you’re looking at the sky until a bird or plane soars overhead.  

Like a conductor of nature, Turrell says that the sky and light are his materials for art, rather than the cement and plaster he uses to create the spaces that let them shine.