I visit Kerkouane as part of my 2 week road trip in the northern half of Tunisia. (I ticked of all the WHS/TWHS there). Kerkouane is a 2.5 hour drive from Tunis or 3 hours from Sousse. I recommend visiting it on the way from Tunis to Sousse or the other way around. Saves you driving the same road twice and Cape Bon is nice to drive around too.

It's a beautiful site and I really enjoyed walking around the site. It's only foundations left, which are in general from almost nothing up to over a meter high. The grid layout is good visitble and you get a good idea how the city must have looked like. Lots of plaster is in tact, mosaic floors (simple ones), and some houses have good signs with explanations and a 3D model how they must have looked like. Great way to explore.

I recommend walking along the coast to the back, walk the small part through the bushes too, until the wall. Then turn right along that road that went to the sea. Then again right over the main road to the main square. This way you see all. The museum on the site is beautiful too.

A small extra, go also to Kelibia Fort. It's nearby and you can manage it the same day. It's nice especially with kids.