If you thought building a house on top of an extinct volcano was cool, how about building one on the inside? That’s what artist James Turrell has been doing on Roden Crater, in Arizona, for the last 40 years.

Roden Crater is an extinct volcanic cinder cone, located in the San Francisco Volcanic Field near Arizona’s Painted Desert and the Grand Canyon. The cone is 3.2 km wide, 600 feet tall, and is approximately 400,000 years old. The volcano and the surrounding land was purchased by Los Angles-based artist James Turrell in 1979, with the intention of turning the cinder cone into a massive open air work of art consisting of a naked-eye observatory at the inner core, where guests could view and experience sky-light, solar, and celestial phenomena.

Photo credit: James Turrell