The Erehwon (UESC-190484) was a Class 3 Heavy Cruiser belonging to the United Earth Colonisation Team, aboard which a population of humans evacuated Earth to form a new colony on Gliese 581d. It had at least four decks.
While the majority of the colonists slept aboard the Erehwon, their new city was built around the ship by the Vardy. (TV: Smile)
Behind the scenes
Erehwon is "nowhere" spelled backwards.