Nefta offers the opportunity to observe desert culture (nomadic people) and oasis life (it has a beautiful, green date-palm garden).
It's also the center of Sufism in Tunisia. It has a nice hotel, too (Hotel Sahara Palace). Although we enjoyed our three nights, there's really very little to do but watch local life and take a camel tour of the oasis. The market is held on Wednesday.
240 mi/385 km southwest of Tunis.