Route 128 retains the north-south alignment of Route 127 as it proceeds south past a pair of islands with one Trainer each. The route turns to the southeast as it swerves to avoid the top of the Seafloor Cavern. On the east side of the cavern's surface, Route 128 splits into two paths, the main north-south path and an east-west path leading to the base of Ever Grande.
The main path of Route 128 continues southwest from this junction, passing two more islands and a Trainer before turning to the south and becoming Route 129.
Ever Grande connector
To bypass an island located due east of the path's western terminus, the connector heads to the northeast, then to the southeast before taking on an easterly alignment near a large island playing host to a Fisherman. After passing a Triathlete, the path enters the city limits of Ever Grande a short distance to the east.
Most of the western portion of Route 128, including the area around the Seafloor Cavern, contains underwater passages that can be reached using Dive. The entrance to the Seafloor Cavern is, fittingly, on the seafloor near the southern terminus of Route 128. North of the cavern, the underwater passage continues onto the seafloor of Route 127.
All items on Route 128 can only be accessed with the use of Surf, except for the Heart Scale on the island with the route sign in Omega Ruby and Alpha Sapphire, which may be accessed using Fly (after visiting Ever Grande City) or Soar.
Route 128 briefly appeared in The Vision. Like in the games, Seafloor Cavern is located here. It was shown in a vision that Courtney had. In the vision, PrimalGroudon appeared from Seafloor Cavern and caused destruction at Route 128 by using Solar Beam.