This sidequest consists of two parts:
This is a large level full of various paths you can take. Your goal here is to find and pull three levels: one red, one green, and one blue. Once you've pulled all three levers, the exit in the top-left corner of the castle will be available.
The levers are in the bottom-left, bottom-right, and top-right sections of the level. The bottom-right lever will require first hitting a switch (after entering a door near the entrance of the level), which raises the water level.
At the exit of the level is a permanent powerup: a pair of Winged Boots. Collecting these unlocks the trophy and grants you the permanent double-jump ability. If you pick up a double-jump powerup (the green powerup), you'll be able to triple-jump, which grants another trophy.