Nationally, U.S. 178 starts at U.S. 78 near Ridgeville, S.C. 

Near the state line, 178 runs near Sassafras Mountain, the highest point in South Carolina (elevation 3560). As with U.S. 276, South Carolina handles most of 178's rise up the Blue Ridge Escarpment . The ECD is located a fraction of a mile into N.C. on 178, rather than at the state line as on 276. 
 

For many years 178's northern terminus was in the center of the village of Rosman. Around 1980, a new U.S. 64 was built around the north of Rosman. When 64 was finished, 178 was extended the short distance north to meet the new 64.
 

178 is U.S. 276's little sister: benign (at least in N.C.) but much shorter. They're essentially twins ascending the Saluda Mountains, although 276 is a bit twistier. Like 276, 178 received mention in Car and Driver's recent "Ten Best Roads of the Southeast" list.[1] 

If you wanted, you could extend 178 north along N.C. 215, but that sounds like an idea from someone who's just looking at a map, rather than someone who knows about the area. 215 doesn't go anywhere; there's no point extending a U.S. highway along it. I'd go the other way instead: kill 178 in N.C. and call it N.C. 215. 

South Carolina has four similarly-numbered U.S. highways: 176, 178, 276 and 278. They all run north-south, and are located in the same region. (There's also U.S. 378, which runs east-west.) It took me forever to keep them straight; how the majority of South Carolina remembers them is a mystery.