Ripley's Aquarium inside Broadway at the Beach is the best non-beach attraction in Myrtle Beach for families. The collection includes a long underwater tunnel where sharks, rays, and large fish swim overhead, touch tanks with horseshoe crabs and other shallow-water species, and a genuine diversity of marine life from the Atlantic coast and tropical oceans. The operation is commercial but competent — well-maintained tanks, good signage, and knowledgeable staff.
Admission is not cheap, but the aquarium is large enough to fill a couple of hours. Arrive early in the day to avoid the worst of the summer crowds. The tunnel section is the highlight: the sharks directly overhead are reliably impressive.