Trove

First I would recommend checking out my solution for destroying 5,000 blocks. You can either read what I have to say, or check the solution for 1,000,000 blocks destroyed as it's faster but will require a different character if you don't already have that one selected.



After you have destroyed 1,000 blocks (Recommend just waiting until you have 5,000 but not required), simply press or hold to place them.

To speed things up, you can place them randomly around the world and if you're backing up, you can get into a good rhythm of backing up and Holding and letting go at the right moment. The trick is to hold just long enough so you can place enough blocks but not too long where you're path is blocked or you traveled too far. If you would rather, press a bunch of times, that works too.

This achievement shouldn't take you that long to do compared to actually destroying and collecting the blocks.