Under the Moat
In the goo beside the huge sand castle in Goo Lagoon, there is a toll clam. Patrick can pay this clam, which spawns a button in the goo. Throwing a melon at the button raises the Over the Moat spatula from under the goo, along with a path leading to it.
With an active Cruise Boost, SpongeBob can clip out-of-bounds at the top of the castles gate, behind the wall of tikis. From there, the player can navigate the terrain underneath the castle. SpongeBob can collect the spatula from below the goo.