Mohhamadieh Citadel is a ruined hilltop fort just outside Na'in, above the village of Mohhamadieh. The remains are simple, but the climb gives wide views over the village, the old cave dwellings, and the dry desert plain beyond.
It is a good add-on if you are already exploring Na'in's older buildings and want a less polished stop. Wear sturdy shoes, as the approach and ruins are rough rather than museum-like.