Not only are the characters named after prisons but they reflect the prisons themselves. Example: Kazan (the mentally challenged character), in Russia is a disorganized prison. Rennes (the "mentor") was a jail that pioneered many of today's prison policies. Quentin (the detective) is known for its brutality. Holloway is a women's prison, and Alderson is a prison where isolation is a common punishment. Leavenworth runs to a rigid set of rules (Leaven's mathematics), and the new prison is corporately owned and built (Worth, hired as an architect).
Director Vincenzo Natali directed a follow-up short film in which we see what is outside the cube. Natali has made a solemn vow never to reveal what was outside the cube, and destroyed the video years ago.
All of the characters are named after prisons: Quentin (San Quentin, California), Holloway (England), Kazan (Russia), Rennes (France), Alderson (Alderson, West Virginia), Leaven and Worth (Leavenworth, Kansas).