You’ll need to beat the game, load your subsequent save file, and return to the World Within before this objective will become available to you. Because of that and the zodiac chests, which do not appear until you have finished the game, none of the Treasure Hunt objectives can be completed until the post-game. This guide will cover where you can find all the initial treasure chests, found in the main game.
For the zodiac chest locations, please see our guide for objective 43.
There are 8 chests to find throughout the World Within (not counting the zodiac chests).
Related: Kingdom Hearts HD 2.8 Final Chapter Prologue Review - PS4
#1, Main area
#2, Main area
#3, Endless staircase; third stairwell
#4, Mirror with many chests; it’s the only chest seen in the mirror as closed (see objective 28).
#5, Dwarf Mines; must move pathway at the end to the floating rock (two images)
#6, Dwarf Mines; to the left of the mirror at the end
#7, Pillar labyrinth; First time upside-down, next to the pillar you just smashed
#8, Pillar labyrinth; Second time upside-down, near the mirror to leave