Can you identify @HughPearman‘s final choice from this photo?

Let us know what building this is by tweeting @WhatBuilding to win a prize.*

*There is no prize

Royal Saltworks

The Royal Saltworks of Arc-et-Senans, near Besançon, was built by Claude Nicolas Ledoux. Its construction, begun in 1775 during the reign of Louis XVI, was the first major achievement of industrial architecture, reflecting the ideal of progress of the Enlightenment. The vast, semicircular complex was designed to permit a rational and hierarchical organization of work and was to have been followed by the building of an ideal city, a project that was never realized.