Title... :-)

Its so obvious, get a bomb do the water obby and bomb the wall.

Not that hard

There's an obby near the beach but you need dynamite to even get to the pearl egg. Dynamite can be found near the digsite.

At the beach, there is an Island with palm trees on the right wall in the sea

1. 
   

   Before you go there, go to the Desert dig site. Get Dynamite from the NPC hidden behind one of the pillars

   
   


2. 
   

   Go to the right side of the beach, there will be platforms appearing and disappearing due to the water raising and descending, just move your camera under the water to see said platforms

   
   


3. 
   

   Once you're on that Island, blow up the wall with your Dynamite (touch the wall), and there will be a chest inside

   
   

Why did you steal my whole fit?!