The "Great Wall" Of Space: Galactic Superclusters a Billion Light Years Away Extend for 5% of Observable Universe
The vastest structure ever is a collection of superclusters a billion light years away extending for 5% the length of the entire observable universe. Insert "yo mamma" joke here. If it took a God one week to make the Earth, going by mass it would take him two quintillion years to build this thing - far longer than science says the universe has existed for, and it's kind of fun to have those two the other way round for a change. Though He could always omnipotently cheat and say "Let there be a Sloan Great Wall."
The great wall is a massive array of astronomical objects named after the observations which revealed them, the Sloan Digital Sky Survey. An eight year project scanned over a quarter of the sky to generate full 3-D maps of almost a million galaxies. Analysis of these images revealed a huge panel of galaxies 1.37 billion light years long, and even the pedantic-sounding .07 there is six hundred and sixty billion trillion kilometers. This is science precisely measuring made-up sounding numbers.
This isn't the only wall out there - others exist, all with far greater lengths than width or depth, actual sheets of galaxies forming some of the most impressive anythings there are. And these walls are only a special class of galactic filaments, long strings of matter stretched between mind-breaking expanses of emptiness.
The immensity of existence truly defies human understanding - which makes it very humanly awesome of us to try anyway. If people could understand for a single second the true scale of everything out there, all our idiotic problems would evaporate instantly. (Either because we got our acts together or our heads popped, no bets on which.)
A Map Of The Universe http://arxiv.org/abs/astro-ph/0310571