Rustaq is 130km south of Sohar via the mountain road and is one of the most rewarding half-day trips on the Batinah coast: a large Omani fort (one of the biggest in the country), hot springs at Al Thowarah, and a traditional souk. The drive through the Hajar foothills is attractive.
Nakhl Fort, 100km south toward Muscat, is another worthwhile stop: an imposing fort on a rock outcrop and natural hot springs at its base. More accessible from Muscat but reachable from Sohar in around 90 minutes.
Wadi Heebi, 65km inland, is a green valley with an old agricultural village — a quiet detour if you have a 4WD and time to spare. The copper mining region in the Oman mountains is historically significant but requires a guide or good local knowledge to visit properly.