In Guezzam is Algeria's southernmost town, sitting right on the border with Niger. For overland travellers heading south across the Sahara, this is the last Algerian stop — though the border has been closed intermittently for years due to instability in northern Niger, particularly Tuareg unrest that Algerian authorities feared could spread across the border.
When the border is open, the route continues south through the Niger border post at Assamakka, then 200km of piste to Arlit and on to Agadez. The unsurfaced road is passable in a normal car but a 4WD is strongly recommended. On the Algerian side, there are flights and a weekly bus connecting In Guezzam with Tamanrasset to the north.
Check the current border status before planning a crossing — closures can last years.