I know the point of view I am going to give will seem oh so hackneyed. I suppose it must already have been applied to the very same particular case that I will be considering; and many times so, even, but all of these times have remained as obscure as they rightly deserve — uh, I mean, dark forces conspired to keep the truth from being revealed to the unsuspecting public. Still, at the cost of my mental sanity, I will reveal to you how you too can see the great Cthulhu the way H.P. Lovecraft first discovered it. Not that I could refrain from telling you, anyway.
Ponder that: It's a monster. Its body changes size. It has two great horrible eyes the lids of which are closed: it is currently sleeping deep beneath the water; but you know it will raise from these depths someday. On its face, countless tentacles make a chaotic mess. Attached to its shoulders, two immense wings fold and unfold. As it moves around you or as you move around it, you see its shape change according to uncanny angles unlike anything else you may observe in this world.
Got enough of that unspeakable horror? Well, relax and take a bath. No, just a shower won't do. Let hot water fill your bathtub, and then let yourself sit comfortably in it. Now bow your head and look down. And there, you'll have a vision! You don't get it yet? Move and adjust your position a bit. Still don't get it? Re-read the preceding paragraph, one sentence at a time, and return each time to your comfortable position, until the illumination comes.
Some of my readers won't be able to see Cthulhu at all, though they might be able to see another of these unspeakable horrors instead: Shub-Niggurath. If that's the case, you still can see Cthulhu the proper way, but that requires the proper ritual, which involves a proper partner — or more than one, for a real black mass — and all the attendants getting in the mood of a wild primitive transe. I would gladly volunteer to show you, but I know such things only happen when the stars are right. Now, some sorcerors know how to make the stars right; but I'm not one of them — yet.
Oh, and if you still don't get it, then think of what unspeakable horror an inhabitant of early XXth century puritan New England would have learned to fear. But don't you dare utter the name. Instead consider that group of cultists who try to raise Cthulhu from the sea with rhythmic chanting...