He needs to chip away half of the stones at the bottom of pillar to make it drop down - perfectly levelly - so he can get through.
Once you've picked out all the blocks you want to pick away at, touch the 'Submit' button to destroy them and let the blocks above fall down in their place.
There can't be any gaps, and the pillar must drop exactly to the halfway point.
But nothing can block true love!
Answer for 'Pillar Problem 21'
The answer is as follows.