The 18th-century Saline Royale (Royal Saltworks), now abandoned, is surely one of the most elegant factories in the world.
The Saline Royale, which was constructed in the 1700s, is no longer in use. 
mnli hypothesis: The Saline Royale, which was constructed in the 1700s, is no longer in use.  premise: The 18th-century Saline Royale (Royal Saltworks), now abandoned, is surely one of the most elegant factories in the world.