Chott el Djerid is the Sahara's largest salt pan: 250 kilometres of cracked crust end to end, 20 kilometres across even at its narrowest, with a single causeway running over it between Tozeur and Kebili. Driving that causeway is the whole point. Salt runs to both horizons, and the heat sitting on it bends the light into fata morganas — lakes, islands and floating silhouettes that stand on the skyline and vanish. The crust is not plain white either. Salts and brine algae tint it green, rust-brown and pale violet in bands that change from one kilometre to the next, and shallow brine pools beside the road glow pink and turquoise. Under 100 millimetres of rain falls here in a year and summer air passes 50°C, so brine seeps up from below and evaporates on the spot, leaving its minerals on the surface.
At the lay-bys, stalls sell salt crystals and the gypsum flowers called desert roses. Twenty minutes' walk off the road southwest of Nefta stands a small white dome: the Lars Homestead exterior from the first Star Wars, rebuilt in 2012 by fans who crowdfunded the repair. The pan was very nearly a sea instead. A nineteenth-century French scheme would have flooded it with water piped in from the Gulf of Gabès, and it died on a survey finding — the floor lies 15 to 25 metres above sea level, not below it. Chott el Djerid has been a Ramsar wetland since 2007 and sits on Tunisia's UNESCO tentative list. When winter water stands on the crust, 3,000 to 15,000 greater flamingos move in and probably breed, the only place in the country where they regularly do.