Prepare to spend a day driving along the east coast from Sur back to Muscat. The distance is very manageable at a bit over 250km, but the time is spent at many stops en route. Highway 17 is well-paved with fairly sparse traffic, but expect speed cameras everywhere.
The first stop is Qalhat, once a major port but now a small village with the ruined Bibi Miriam Mausoleum. Until the end of the 15th century, the hills brought water to this area, and the small lagoon offered a good place to drop anchor. An earthquake destroyed the city, then the Portuguese invaded, killing the population and burning everything else.
The mausoleum sits on top of the hill overlooking the once great city. Unfortunately, it is closed and there is a lonely guard on site watching the crumbling ruins.
From here, it is not a long drive up to Wadi Shab, a must-see so you will likely be overwhelmed by tourists as opposed to locals. The first challenge is to find a parking spot.
After finding that difficult parking spot, the next step is to walk to the river mouth under the highway bridge. Small boats take you across to the other side for 1 rial, where you can start the 3km walk into the wadi.