Return and continue the path. Go passed Challenge 3 to the puzzle where you have to turn the various pipes to get down. There's one chest with the blue button.
After that puzzle, you pass another battle area (Challenge 4) and get to a platform, where you have to DIG! some ground to be able to MOVE! a block onto the Red Square. This unlocks the Cannon. Take it.
Now go down the pipe and continue the story. Cross the big battle area and you'll get to some blocks. There are movable blocks on the other side. Move them in a mirrored way. Don't forget to push one down...
Continue until you see a box to move in front of the pipe to the left. Move it down and take the pipe. On the other side, move the Box again until you can take the next pipe.
Pick up the statue on the way down and go up to put it on the yellow pedestal. Then keep pushing down the block, get the same statue from above and put it on the blue pedestal. Now you can access the last 3 chests.