# 220 black squares (but that's not the point)

Some hints for this question have been embedded in this challenge: Counter-Red Spiders.
...though that is a standalone puzzle.

The title technically describes this puzzle. There are, after all, four grids here outlined in black. Each is itself a square from which you can also make 4 4x4 squares, 9 3x3 squares, 16 2x2 squares, and 25 1x1 squares; for a total of (25 + 16 + 9 + 4 + 1 ) * 4 = 220. But that's not the point. There are 900 black rectangles, but that's not the point either. Honestly, it's just a title; it had to be called something; and the puzzle per se has a lot of elements in it, but they are all meant to be discovered, not spelled out.

Obviously there's a cipher here somewhere; figure it out. If you need hints, they're already included in the puzzle.

I will tell you this... the solution to the cipher is a piece of advice; but it's really terrible advice as advice goes. It's just themed. I'm not here to change the world; I'm just here to entertain some wary traveler for a while.

• Ooh, this is interesting. I think I've already figured some things out. – Deusovi May 20 '18 at 20:11
• Progress update: I think I've found the word HAZARD as one of seemingly many important words. – Deusovi May 20 '18 at 21:03
• Another progress update: 12 placed. Gradually becoming easier. – Deusovi May 20 '18 at 21:37
• I had misplaced something, but that did confuse me - thanks for the clarification! I'm now trying to figure out what to do with this information... – Deusovi May 20 '18 at 22:26

In the image:

there are two types of off-white pixels. Here I've replaced FEFEFE with blue and FFFEFF with yellow (and for the rest of this post I will call them "blue" and "yellow" for simplicity).

There's a common motif throughout the image:

four blue pixels in the corners of a 3x3 square, with one yellow pixel in the 5×5 box surrounding centered in the same place (sometimes overlapping!). I will call each one of these patterns a "grille". Using the top right region, we can figure out what these grilles mean.

Analysing the top right

Here's the top right of the image, resized. Looking at the three rows, we notice they're offset suspiciously. In fact, these make a QWERTY keyboard layout! If we put the letters in the corresponding positions, we get:

A B C D E
F G H Ĳ K
L M N O P
Q R S T U
V W X Y Z
This seems to be the square used in the Playfair cipher (without a key), called the Polybius Square.

Reading off the bottom part by the "broken pitchfork" symbol, we get the phrase FOR KEY. So the pitchfork is the key, maybe? I'm not sure yet.

Next we turn our attention to the empty blocks.

By that I mean the giant blue regions. There are 17 of them; add the 8 yellow symbols below and you get 25. In addition, it looks like most of them have three grilles on each side, but some are missing them on one (or even two) sides. This hints that the pieces can be assembled into a 5×5 square. All the corners are in the same orientation, so they may have to be turned, but luckily we don't need to flip anything (because the grille placement isn't symmetric).

Solving the Jigsaw Puzzle

But how do we assemble them? To make words! For instance, two of the symbols combine like this:

to form the word HAZARD in the center, according to the code from the keyboard.

Over the course of nearly an hour and a half, I pieced things together to get this:

One helpful addition is that each of the rows and columns of words is made up of a six-letter category, plus four members of that category. For instance, the column between the first and second column of squares has the words YELLOW ORANGE PURPLE VIOLET COLORS. The others are:
Column 2-3: KAHLUA MOJITO FRAPPE EGGNOG DRINKS
Column 3-4: PAPAYA RAISIN BANANA CHERRY FRUITS
Column 4-5: FENNEL NUTMEG WASABI GARLIC SPICES
Row 1-2: SIGNAL BEACON HAZARD BUZZER SIGHUP
Row 2-3: OBJECT PLANET PULSAR QUASAR NEBULA
Row 3-4: ANIMAL HORNET TURTLE RABBIT JERBOA
Row 4-5: ZODIAC TAURUS PISCES CANCER GEMINI

The categories are all in the bottom or left parts of the grid; the bottom row and left column happen to not have any of the symbols. I'm not sure whether this is a coincidence.

Now what?

We still have the four visible grids to deal with. It seems like the symbols (besides the pitchfork) can be associated with letters once again using the Polybius square, but they don't anagram to anything or seem meaningful if we replace them. The lower-left grid's symbol doesn't appear anywhere, and I'm not sure what it means.