It was mostly grey, about the size of a small village, and the fillies and colts liked to watch it sometimes. Some of the slightly older ones, those in the age where one tends to think of oneself as older than they are, occasionally dared each other to slip a hoof inside, or quickly jump in and out of the outer rim. No one ever did though. And they all knew better than playing near it, lest they lose some toys inside it.
It was cold, just to stand at the edge of it. Unnaturally cold. Even in the most scorching of summer days, it still sent chills down creatures' spines that no one wanted to experience. It wasn't safe to drink near it, or touch anything made of metal, and birds and other animals had long since learned to avoid it while travelling. Very rarely, someone came from around Equestria to see it. Even more rarely did they not regret the decision.
There was a section of it, just a bit, that was still inside Canterlot. But no one went there. No one lived in the portion of the city around it, and no one had any interest in getting close to it. A few said the cold grew even stronger there, and though no one bothered to check, no one doubted it was true. The rest of the city was still in use, if not as lively as it had been before, but that area was completely deserted.
Not that there would have been anything to see. All the trees had died, just like all the grass and flowers. The buildings had crumbled and turned to dust. The ground inside it was naked, grey, lifeless and cold. Flat, featureless earth, like the fresh layer of skin beneath a wound. No one had bothered to check how deep it went, but after all the time it had been there for, everyone guessed it would be pretty deep. Trees around it didn't grow on the side facing towards it, especially the older ones, and digging they'd found their roots had died and withered on those sides.
Every once in a while, one of the few, more determined researchers attempted to study it more in depth. Oftentimes someone from Princess Twilight's institution, the only place with any considerable resources for research. And they always failed. And so, for a couple days, citizens were treated to the sight of abandoned equipment right past the edge. Then, that disappeared too. No one knew when, or where it went, no one had any interest in finding out.
One time, Twilight herself had come to see it. She'd brought no equipment, no materials, and no one else with her. And she'd sat there, for a couple of hours, looking at the strange, abandoned, deserted land where the Behemoth cast its shadow. Then she'd left, without saying anything. She hadn't gone to the opposite end of it either. There in Canterlot, where the shadow began, where the Behemoth still stood undisturbed over the city, like the day it had first come there.