There are 2 cells for 5 prisoners. The walls regenerate with cobblestone. There is water on the floor. Visitors fall in from the ceiling while prisoners respawn from below.
More Security
The roof detector triggers a long chain of pistons pushing 12 blocks down. The floor detector also triggers suicide. Above the floor detector there is some pearl glitch prevention. Around the prison are wither walls and columns of mob bans. There are 8 trap portals that trigger suicide.
