[sionnsar]

Up to Castle 12.

[Darksheare]

I crushed all 24, then built a test one or two.
Cantilevered castles sometimes stand up to large rocks but not bombs.
And sometimes large thick walls stand up to bombs but not big rocks.
Depends on the angle.
One of those you have to drop the rock into the hole onto the target.

[Darksheare]

Level 13 is the one where you have to drop the rock into the hole.