Sun Tunnels are large, cylindrical structures made of concrete that are located in the Great Basin Desert of Utah. Designed by artist Nancy Holt in 1976, these tunnels are aligned with the sun's path during the summer and winter solstices, allowing sunlight to illuminate the interior at specific times of the year. The installation consists of four tunnels, each measuring 18 feet long and 9 feet in diameter. Visitors can walk through the tunnels and experience the changing light patterns, which create a unique connection between art, nature, and the passage of time.