These sun tunnels were built by artist Nancy Holt between 1973 and 1976. She explored the human perception of time and space, earth and sky. The art project consists of four tunnels formed from massive concrete tubes and laid out in an X shape. Each tube is drilled with holes to pattern the constellations of Draco, Perseus, Columbia, and Capricorn.
The artist said, that the tunnels bring the sky down to earth, with the sparkling effect of light bouncing through the tubes. Two of them align with the setting and rising sun during the summer solstice and two line up during the winter solstice.