Ironlock Prison is abandoned prison located in the Dark Swamp. It is the only structure in the area. its main entrance lies across a deep gorge, spanned by a rotten wood drawbridge. It resembles a foreboding castle, and even Sonic claimed that it looked creepy. The prison gate has a massive wooden door surrounded by a stone wall.
As shown so far, Ironlock is in serious disrepair, with crumbling walls and ruined buildings. Inside the prison there are different floors and cells. Where it remains intact, it can be seen that there are various types of prison cells. Some doors and cells are made by metal bars, while others are made of stone block walls, and have reinforced wooden doors. One prison cell in particular has an old computer left inside it. The prison is also connected to Robotropolis by underground tunnels.
In the present day, Sally and Antoine traveled to Ironlock Prison after Nicole received a message (probably left by the King) that originated from that location. After arriving at Ironlock Prison, the heroes carefully walked across the building's drawbridge, but when it began to collapse, Antoine took Sally's hand and quickly ran to safety on the other side before the drawbridge caved in. The heroes then went inside Ironlock Prison and found a torn piece of the King's cloak there. Soon after, they reached a cell with an old computer inside it. In the meantime, Sonic got inside Ironlock Prison after jumping across the gorge in front of the entrance, and met up with his friends. Sonic, Sally and Antoine, with the aid of Nicole, proceeded to decrypt the computer Sally and Antoine had found, which bestowed them with a map of the underground tunnels underneath Robotropolis. Shortly thereafter however, they activated a trapdoor right below them. After they fell into an underground tunnel, a monster attacked them. Using a Power Ring however, Sonic destroyed the monster, which turned out to be a robot. Afterward, the heroes reached an underground tunnel that led them back to Robotropolis.