While itself not an amazing Roman building, I also enjoyed going to Ksar Ghilane - https://maps.app.goo.gl/Ru5sEqEtJDEWNg3R7. There's a small touristic oasis where you ran rent a quad bike, zip over some dunes in the Sahara, and then stop at the small Roman fort. It's fun to imagine being a Roman stationed at one of the southern most outposts of the empire. It's also fun to rent a 4x4 w/ driver and drive through the desert from Douz to Ksar Ghilane.
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