Hello everyone,
amazing tour, this will probably be one of my favorites.
From Marseillan Plage to Sete, the route goes along the sea on a tarred cycle path. The climb to Mont Saint-Clair takes about 20 minutes with gradients of up to 17%, but once you get to the top, you are rewarded with a fantastic view.
As you can see in the picture, you could go to the small restaurant to get some refreshment. Once you get back down, the route goes left-handed through the super beautiful town of Sete. From Stete, the route goes around the lake on tarred cycle paths until just after Meze, where you should have something capable of off-roading under your saddle. In the port of Meze, you can refresh yourself again in one of the small restaurants.
Don't forget to take enough to drink with you, though, and remember that there might be a strong headwind.
Other than that, I hope you have a nice day.
Best wishes, Marcus