It appears to be just a sandy field with brain corals everywhere. There is also a sign which reads "Brain Coral Fields."
The plot occurs when SpongeBob spots a sign revealing that there is a dangerous cliff behind, which Patrick cannot read and runs straight towards the sign, smashing into it, and falling off the cliff into a place known as the "Brain Coral Fields." SpongeBob pulls out something that looks like Patrick's head but is actually a piece of brain coral which made a plug into Patrick's body and makes him extremely intelligent and brilliant.
After several unsuccessful attempts of getting Patrick to play childish games with him again, SpongeBob feels depressed about Patrick's behavior from before, in which the latter says he can no longer be his best friend anymore. It is then revealed that Patrick was willing to end his intelligence for the sake of friendship with SpongeBob.
The two are then shown back at the place where the plot began, and Patrick decides to run towards the sign again, and discovers Brain Coral Fields once more. Patrick then tells SpongeBob where he found his head, which SpongeBob points on his side. Patrick measures the place where he crashes and then calculates that his actual head was three meters to North. SpongeBob then takes out the brain coral on Patrick's head and plugs in his old head again, in exchange for his smartness. The episode concludes happily and the two finally became best friends again.
The brain corals resemble Patrick's head.
There is a real coral called brain coral, although it looks completely different.