Paradise is a "heaven-like" world where those who have paid their respects to TITAN go once they have fulfilled TITAN's needs. It is where TITAN supposedly lives, and only the highest-ranking followers are permitted to follow TITAN into Paradise. To go to Paradise is the goal of every follower of TITAN. Strategos Six seems to live in Paradise as well.
MentionsParadise is first mentioned through Gil Marverde when he explains his wishes to be a doctor. Doctors have a high status among the ranks of followers, and thus could very likely gain access to Paradise once their service to TITAN has been fulfilled. He hopes that when he goes to Paradise, he will be able to ask TITAN for help on figuring out who Nevy is and where she came from.
Strategos Six is mentioned to have come "straight from Paradise," and introduces the Gate to Paradise as a machine that will give followers an "eternity to reach Paradise."
Prudith mentions that she will look down at Ava and other Titan failures from Paradise. This seems to indicate that Paradise is in the sky, or otherwise tall.
Not much is known about the history of Paradise. No proof of it exists, other than what has been told to Gil, Prudith, and many other followers. It is described as a heavenly utopia for followers, but other than that, it is shrouded in mystery. Odin, along with some other characters, is skeptical of the idea of Paradise and doesn't believe in it.