The night sky looks as smooth as the surface of a calm lake. But if you look at gamma-ray bursts (brief, blinding explosions visible across the entire universe) you'll find ripples in that smoothness.
Scientists took a catalog of such bursts and divided the sky into two hemispheres. In the southern one, they found a tiny group: 4–5 bursts huddled together. Two of them, GRB050822 and GRB050318, turned out to be close not only in the sky and in distance from us but also in observation time: they were detected just five months apart. Like two shots from the same rifle.
This doesn't mean the cosmological principle, the idea that the universe is homogeneous on large scales, is wrong. It's just that large clumps of matter, like this wall, can slightly alter the picture: where there are more galaxies, gamma-ray bursts are born more often. The new testing method found no other deviations from uniformity besides these two groups. The calm lake remains calm, except for two noticeable waves.
The Hercules–Corona Borealis Great Wall is so vast that light takes about 10 billion years to cross it from one end to the other.