Curious Caverns
"Curious Caverns" is a 
"The Island Mystery" quest that is unlocked the next reset after completing the "Revive the Oasis" quest.
Quest Description
"Explore a mysterious cavern revealed by the restoration of the Oasis..."
Quest Information
The player meets with 
Pompompurin, who was enjoying the view of the 
Oasis and reminisces about the time his 
Dessert Boat was on the ground, but comments that it is better and even more 'boat-like' now that it is floating on the water. While taking a stroll, he noticed the waterfall knocked a few rocks down and urges for the rocks to be removed as the rocks are unstable. He says that he would do it himself but needed a nap after his stroll.
Pompompurin then brings the player to the location of the Rockfall, where the player has to use their 
Pickaxe to break the Rockfall. After which, he says that they can walk through the waterfall and although he wants to take a nap, he does not want the player to be left alone. Therefore, they walk through the waterfall together.
After emerging from the waterfall, Pompompurin and the player end up in the 
Merry Meadow, where the quest ends.
