4×4×4

After a number of X×Y×Z crosswords, we finally have one in 3D! The grid represents four 4×4 layers, stacked on top of each other (in the order NW, NE, SW, then SE). That means every cell is triply-checked (at a minimum). At the ends of the clues for the entries in the topmost (NW) layer are the clues for the four entries that begin in that row/column of the top layer and intersect the other 4×4 layers. For example, the clue for 1A includes the regular definition, then clues for the 'vertical' words starting in the cells marked 1, 2, 3, and 4, and the 'vertical' word starting in 1 goes through the cells 5, 15, and 19. Got all that? Phew! One of the 3D diagonals will describe the crossword as a whole.