A major feature of "3D Number Place" is that it is usually not possible to fill all cells with just one face hint cell. It's not just about solving the six-sided Sudoku. The numbers are the same as the surrounding cells of the faces that the surrounding cells of each face touch. Some surrounding cells cannot be solved without looking at the columns, rows and blocks (3x3) of the other faces that touch the cell. The rules are the same as for Number Places (also known as Sudoku), where you have to