Approximate playtime for this cheeve, from the beginning of the game: 2-3 hours.

IMPORTANT: SAVE YOUR GAME AFTER EVERY MAP SQUARE!! THERE IS NO AUTOSAVE!
This game can crash, and you will lose your progress unless you save regularly.

The ability to break blocks is awarded for beating the 3rd Boss. He isn't hard, but buying the first 4 upgrades from the shop makes it easier.

Make sure you:
• Save up 25,000 to get the "Collect 25,000 Gold" achievement before buying from the shop.
  
• Kill all the enemies along the way, and break the small blue orbs that they sometimes drop to collect the power-ups, to get a total of 100 for the "Power Up" Achievement.

Follow this map:


The 3rd Boss resides in the Asian-looking Temple on the world grid, 5 blocks down and 2 blocks from the left, and yes, you have to beat the first two bosses to get to him. It might take you a couple hours to get there.

In the above map, I have marked 2 squares which are ideal spots for griding out this cheeve.
***Note: Thank you to user Berserk for suggesting the lower square containing 24 blocks!

After beating the 3rd boss, proceed to either of those squares:

I did the cheeve on the upper square of 13 blocks:

Break the orbs till you hit 250 objects smashed. The game keps a hidden count, so when you get to 250, your cheeve should pop:


Rate this up if it helped you!
GLHF, and happy cheeving!
ruddy

Thanks again to Berserk for suggesting a square with even more blocks clustered together! :)