Obi-wan Kenobi: That's no moon... It's a space station.
Han Solo: It's too big to be a space station.
Warhammer 50,000 - Mankind has taken to the stars in a ship of unimaginable proportions. Cannibalising the million worlds of the old Imperium, mankind seeks a refuge from the horrors of this galaxy. Home to untold trillions, the great black ship travels the void, whole decks lit by the light of artificial plasma suns, each room a continent, each rivet a mountain. Humanity lives and dies on a vessel of it's own making.
But all is not well on the great ship Imperius. Legions of Orks thrive in the vast wildernesses of the ships bowels, Tyranids infest it's corridors like cockroaches, Shadowy metal figures make whole sections of the ships unpassable, the miles of empty corridors as still as a tomb. In the crowded markets of the Cabinhives, strangely elegant travellers can be seen wrapped in rustcowls and speaking to no-one.
In this great ship mankind still faces war. Legions of soldiers fight to keep the great arterial corridors open. Millions of men die to defend a single coolant junction. These are the things mankind survival depends on and what it's enemies seek to destroy. But still it journeys on, it's destination only known to the navigator, the Emperor himself.
And if he knows, he is staying silent...