What are Levels?
The tower can be divided into distinct levels, each one on top of the other. Go ever higher. Different levels have different rules: it might take more or less time for bricks to be placed, require more strength, or things yet unknown.
Builders can only put bricks one level above the highest level they've successfully built on so far.If you've successfully put bricks on level 2, you can put bricks on level 3 but no higher. Levels above that can't be seen or built on.