The prisoner is in a 4x4 box with seagrass on the floor. The walls and floor regenerate upwards. The roof is too high to reach. This cobblestone box is in the middle of an obsidian room with lava on the walls. The prisoner respawns from above and falls down due to the 2-chamber respawn system. There are two beacons to heal the prisoner (although those can be easily blocked off by an outside escapist). The visitor uses an ender pearl to get from the corner of the lava room to the cobblestone box.
Outside Defence
There are 8 permanently enabled area kickers around the prison. There are an assortment of lava, bubble columns, and anvils to try to stop withers. Above the prison are two mining detectors, one with sideways observers and one with tripwires. Below the prison is a 3-block-high pearl glitch/squilly detector using tripwires. There are two regenerating trap portals, which may have been the first time those were released in a public prison ¯\_(ツ)_/¯
More Security
In the nether there are elder guardians, and a very tall nether side portal so that if an intruder enters the nether with levitation, they will be unable to then enter the overworld. Unless they use a lava bucket.
