In the heart of the forest, near Milly la Foret, is an enormous head called "le Cyclop" which sparkling with mirrors, is more than twenty metres high. Inside it, there are gears and mechanisms that propel huge metal balls throughout the head, around various artworks and installation pieces.

In 1969 Jean Tinguely, his wife Niki de Saint-Phalle and numerous other artists, began work on this unique, monumental sculpture. It took over 300 tons of steel and twenty years of work to complete. It incorporates works by Arman, César, Raynaud, Rivers, Spoerri, Imhof, Luginbühl, Soto, Weber, Aeppli, Lejeune and Bouveret. In 1987, Tinguely and Niki de Saint-Phalle donated the sculpture to the state and it was first shown publically in 1994.