The trip to Tunisia will be more like Portugal than Ethiopia. There will be some walking - but not long treks.
There is some walking around the archaeological sites in Carthage (some uneven ground), walking around around the village of Sidi Bu Said, and some walking in the Medina of Kairouan. The hotel in Djerba is about 1 mile from the Hara Kabira which is the Jewish neighbourhood. This is the only place one can stay for a Shabbat with the community. We will walk this back and forth on Friday night and Shabbat day. The walk is along paved sidewalks and roads (the roads of the Hara are closed off on Shabbat).
Most other sites are on and off the bus - with some walking around the site.