This is a very interesting site consisting of 2 separate components located near the Swiss border. I set out to visit both places by public transport from Besancon in one day. The train ride from Besancon to Arc-et-Senans is straightforward and very short, and the salt works are just a few steps from the station. As stated in the other reviews, Arc-et-Senans is mostly about architecture and urban planning, and the creation of a model city that was never fully realized. It is very pleasant to walk from building to building, which are set up in a semi-circle, and also to explore the surrounding gardens. The buildings have different purposes, from hotel rooms to exposition space (including a nice exhibit on World Heritage sites), and it takes a few hours to see everything. I then took the train to Mouchard and waited for a bus to Salins-les-Bains that didn't come (apparently I had misread the schedule, because there are fewer buses in summer, during school holidays). The lady at the SNCF ticket counter was nice enough to call me a taxi so that I could arrive at Salins-les-Bains (about a 15-minute drive away) in time for the German guided tour (they started with these this year, and tours are also available in English, at least in summer). They take you underground and give interesting explanations about salt extraction and the lives of the miners; some parts date from the 12th and 13th centuries. Afterwards, you also see a building aboveground that contains original artifacts such as salt pans. In the late afternoon, I took a bus from Salins-les-Bains (which is by the way a very pretty town with a nice historic centre) to Mouchard, from where I caught a train to Besancon. Taken together, both sites provide an interesting overview of the trouble taken to provide people with salt, which is of course not only needed for health reasons, but in the past was also used to cure meat and as a form of payment (where the word "salary" comes from).