The UNSC Spirit Of Fire, a ship from the Halo series, would be 2.5km long if it were a real thing. But it's not. So all we've got instead is this "tiny" model.
Mark Kelso spent four years building this monstrosity, which is based off 3D models and had the insane goal of not just replicating the ship, but designing it so that the exterior didn't show any LEGO studs. This would make it look more like a scale model kit than a LEGO build.
And he did it. This thing is incredible.
UNSC Spirit of Fire [MOCpages]