In 1971 Robert Smithson (1938-73) was invited to create an earthwork in the Netherlands on the occasion of the recurring outdoor exhibition Sonsbeek. Beside a working sand quarry in the province of Drenthe and cut into the side of a terminal moraine, Smithson created Broken Circle/Spiral Hill - his only extant earthwork outside of the United States. Broken Circle/Spiral Hill is an artwork of two parts. Broken Circle is a semi-circular jetty built into the quarry lake; at the center is a huge immovable boulder deposited by ancient glacial movements. Cone-shaped Spiral Hill can be climbed via spiraling path and at the top the quarry and Broken Circle can be seen from above.