The Elysian Gate

The Elysian Gate is a Dark Age warp-door at Uranus, a three-thousand-kilometre open parabola that lets ships skip Sol's Mandeville points. Rogal Dorn hinged the Second Sphere on it; Perturabo smashed the Eyes of the Old God gun-grid and took the gate in the Solar War. Traitor hulls later ran the same aperture into Ultramarines hunters as they fled Terra.