I suggest to see and drive:
1. Tassili N'adder national park with paintings i.e Jabbaren (the closest),
2. cross Assekrem by 2 different ways i.e. from Tam close to basalt pillars and after passing Assekrem in direction to Hirafok (condition of road is bad but the views are nice)
3. further form Hirafok week of driving to Janet by desert (you need 200l of diesel) there are old salt sources, vulcans, sarir, dunes, stones and lack of fuel and water till Janet. distance up to You ca 900km. brilliant trip.
4. we've never seen InSallah's trees due to lack of time but its known and there is no problem to find - as Yves said - ask guide.
5. a lot of more - south of Algeria is nice. And fuel cheap