The prison was created in five times simultaneously, not twelve times.
Ages ago I made an MS Paint drawing for this, but that was back when Photobucket was free and helpful.
The design was like a slinky, but instead of being five points directly above each other, they were spaced so that from above (or below) the slinky, the points were equidistant and formed a pentacle when connected.
Also the prison does have other ties to the number twelve. There were 1,728 steps, or twelve sections of twelve stairways of twelve steps.
Might find this interesting. Found in on the web
The number 12 signifies perfection of government or rule. According to Bible scholars, 12 is the product of 3, which signifies the divine, and 4, which signifies the earthly. The heavenly bodies are also connected to the number 12 since the stars pass through the 12 signs of the zodiac in their heavenly procession. The number 12 has further significance, as it represents authority, appointment and completeness. The number 666 is used to represent the devil and hell, whereas 12, 12, 12 is believed to signify God and heaven. The number 12 is also associated with the government of the cosmos.
Perhaps the 12 sets of sections of 12 stairways and 12 steps in a clue about an Angel being involved with Demon Reach?