To unlock the Rainbow Shell Gallery in Cookie Run: Kingdom, you must reach Castle Level 8, which allows you to clear the land in the bottom right corner and upgrade the Trading Harbor to "Touc's Trade Harbor". Once upgraded, the Gallery appears as a shop within the harbor, allowing you to exchange Rainbow Pearls for rare items like Legendary Soulstones.
The best way to obtain a Rainbow Shell is by foraging on the Beach during the summer. Other methods include purchasing from the Traveling Cart, finding them in the Mines, or receiving them as gifts.
I did complete the request before, because the first quest is putting the battery in the tunnel box, then it says to put a rainbow shell in the train station box.
The Secret Woods are an area available after obtaining the Steel Axe. To get there you have to destroy a large log a few meters above the Wizard's Tower, directly to the west of where the Traveling Merchant appears.
How To Unlock Rainbow Shell Gallery Cookie Run Kingdom (Full Guide)
How do I trigger the Mermaid Show?
When you enter the Mermaid Show, it will automatically start playing, and it will restart if you leave and come back in. The show takes 1 hour and 40 minutes of in-game time to complete.
What happens when you reach level 100 in Skull Cavern?
Floor 100 of the Skull Cavern is guaranteed to contain a treasure chest. The only exception is during the run where the player completes the secret. Floors 200 and 300 of the Skull Cavern are also guaranteed to contain 2 and 3 treasure chests, respectively.
