I visited this industrial heritage in July 2013. Like Paul, I had no idea what to expect or what I was going to see. Well, my visit to Arc-et-Senans and especially to Salains-les-Bains proved to be remarkable to say the least. This became my favourite industrial WHS! The Royal Saltworks of Arc-et-Senans were interesting mostly for their architecture and utopian planning. I learnt that it is also possible to sleep inside the Royal Saltworks as there are a couple of rooms available for 85euros. This means you'll have the Royal Saltworks almost for yourself in the morning before opening hours. However, the highlight of my visit was the Salt Mine and Museum in Salains-des-Bains. You have to visit with a French-speaking guide but an information sheet in English is provided with a translation of the guide's commentary. The guide was really excellent and really gave an interesting tour. The salt mine machinery is still fully functional. Do try the sweets they sell in Salins-les-Bains with the local salt. Yummy!