After you fight some Team Flare Grunts in Glittering Cave and revive a Fossil, you travel along the beach on your way to Cyllage City.
Revisit Ambrette Town
Go down the stairs from the aquarium, then go south along the beach. You will go back to Ambrette Town, but you'll end up on the beach area at the base of the cliffs of town. You will find a Pearl at the end of the path. If you fish with the Old Rod here, you can find Luvdisc.
Battle and Catch
Go north again to Muraille Coast. You can break rocks with Rock Smash to find things like Soft Sand, Hard Stones, and Heart Scales. Breaking rocks might also make Binacle or Dwebble appear. In the water, when using the Old Rod, you can find Luvdisc.
To the northwest, you will find a Mago Berry Tree.
East of there, you find a swimmer who gives you a Dowsing Machine. When you use the Dowsing Machine, it will shoot out beams of light if there is a hidden item nearby. Blue beams mean that you're a few steps away from the item. Green beams mean you are a couple steps away. Yellow beams mean you are one step away. If the beams cross and turn red, you have found the item and can pick it up by pressing A. If the beams of light stop shining, it means you're facing the wrong direction. You can't rollerskate while holding the Dowsing Machine.
Near the swimmer, you can find a Pearl. South of her, there is a hidden Ultra Ball. West of there, you can find a hidden Heart Scale. Near the Mago Berry Tree, there is a hidden Stardust.
If you go south along the beach until you are in the beach area of Ambrette Town, you can find a hidden Rare Candy.
To the north, you are challenged by Swimmer Genevieve. She has a level 19 Wingull and a level 21 Psyduck.
North of the swimmer is Fisherman Wharton. He has three level 19 Tentacools.
To the north, you find Fisherman Shad. He has a level 20 Shellder and a level 20 Staryu.
To the north, Swimmer Marissa is walking around. She has a level 22 Masquerain.
If you go east from Swimmer Marissa and use Rock Smash on the rock, you will find a sign that has an advanced tip about Rock Smash.
Go north from here to reach Cyllage City.