You need Surf and Waterfall. From Route 14, find the karate guy on the bridge over the river. Go left and up the waterfall, then up another waterfall above you. Then go left and down the waterfall across there. Follow the path left to Abundant Shrine.
It's to the east of Lacunosa Town, but there is a boulder in the way. You need to basically loop around. Go down on Route 13 then down the steps to the left and back along the beach, then north on the water and up the steps the other side. Use Strength on the boulder to make a shortcut.