This page offers a walkthrough of Episode 1: Dune Bud Sand Castle Secret in Gelato Beach.
Spray the Dune Bud
When you arrive on the beach, you’ll need to find a Dune Bud and spray it so that the Sand Castle appears. There are a fair few Dune Buds on the beach but you’ll need to spray the one circled below to trigger the spawning of the Sand Castle. The Dune Bud you need is in line with the beached boat, so you’ll come across it fairly easily if you just head down the beach towards the boat. It is also adjacent to a piece of land that juts out into the water (this is where the Sand Castle will also spawn).
After spraying the correct Dune Bud and spawning in Sand Castle, head over to it and walk through the arch to enter into the next stage of this episode.
Falling Sand Path
Inside the Sand Castle, you’ll need to make your way over a long and winding path consisting almost entirely of sand blocks that begin to fall as soon as you step on them. They’re not too hard to run over and they don’t fall straight away, so there is definitely room for a few mistakes. When you reach the end of the path, you’ll then need to climb up a small moutain that is mostly made up of sand blocks. There are two peaks, the furthest away from the path has a 1-up Mushroom and then at the top of the one that hangs over the sand path, you’ll find the Shine Sprite.