The Coastal Road (海岸道 Kaigan Michi) is a field area between the Mythos Path and Port Rimorge. It also has a suspension bridge connecting it to Quatera Island, though the bridge has been destroyed shortly before the start of Ys VI: The Ark of Napishtim.
Upon arriving there from the Adol Christin meets Lloyd and Xaxon, members of the Baslam Trading Company. Their conversation implies that this was one of the areas the Baslam Trading Company took materials from to improve Port Rimorge.