Unbreakable block

Unbreakable blocks are objects in Alleyway that cannot be destroyed with a ball. These blocks are larger than breakable blocks and take up two lines instead of one. The ball bounces off of these blocks. Unbreakable blocks can only be destroyed in the Advancing Block Screen pattern, where they can be removed after reaching a certain point on the screen. It can also cut these blocks in half.

In the first three stages, unbreakable blocks protect the ball from touching the ceiling to prevent the paddle from getting smaller.

Appearances
Unreakable blocks appear in the following stages:
 * Stage 1
 * Stage 2
 * Stage 3
 * Stage 10
 * Stage 11
 * Stage 12
 * Stage 16
 * Stage 17
 * Stage 18
 * Stage 19
 * Stage 20
 * Stage 21
 * Stage 22
 * Stage 23
 * Stage 24

Unbreakable blocks do not appear in Bonus Stages.