Trains, in a way, and the key to 18 of this puzzle's black squares. (Ones that begin with the keyword are asterisked. The others are for you to discover.)

Question:

Answer:

SHADOWBOXES

Length:

Similar Crossword Questions:

Like aleph in the central black squares of this puzzle's grid
Complete set of 12 shapes formed by this puzzle's black squares
Row of black squares preceding or following six puzzle answers, thereby completing them
Web concerns ... and based on six familiar names hidden in rows 1, 4, 12 and 15 of this puzzle grid, what the black squares in those rows symbolize
On hold ... or what the seven rows of black squares in this puzzle's grid spell in Morse code
How this puzzle's black squares are arranged
Dictionary source for each asterisked clue in this puzzle
Like some crossword-puzzle squares
Octet of black squares in the middle of this grid, typographically
The 2x2 black square near the middle of this puzzle's grid, e.g., which is part of eight answers
Movie good guys responsible for the circled squares in eight long puzzle answers
What black and white squares do on a chessboard
Welcome mat spot (our puzzle title hints at the theme revealed by the pattern of circled squares)
Company "sorted" in this puzzle's circled squares
TREASURE HUNT STEP 2 (include black squares)
What the three sets of circled squares in this puzzle represent
Puzzle based on Latin Squares
Number of times this puzzle's theme word appears diagonally in the grid (to complete the puzzle, shade those words plus the Down answers that begin where they meet)
What's been deposited in four squares of this puzzle, expressed both by name and by symbol
What spouse does, step 4 [hint: look at the black squares of the grid]
Phenomenon observed in receding galaxies ... and in the answers to this puzzle's asterisked clues?
Your role in this puzzle [the asterisked clues will help you crack the case]
Term for each of the 15 asterisked theme answers in this puzzle
Black Friday destination found in nine of this puzzle's Across answers
What the highlighted squares in this puzzle represent