The Dark Swamp is a murky swamp covered in dense vegetation. The local trees do not grow well in the deep natural water reservoirs. The swamp is also often foggy and the sky above is covered in dark clouds. There are also robot parts and vehicle wrecks found all over the Dark Swamp. The only structure found here is Ironlock Prison.
In the present day, Sally and Antoine went to the Dark Swamp to find Ironlock Prison and receive a message left there by the King. During their journey through the swamp, Antoine became very afraid of the swampy environment, but Sally encouraged him to go on. After Sally and Antoine reached Ironlock Prison, Sonic began following them. Traveling through the Dark Swamp, he eventually came across his friends' footprints and began tracking them. However, Dr. Robotnik would soon after send a Stealthbot after Sonic. When the Stealthbot arrived, Sonic managed to escape it and destroy it with its own missile. Sonic soon after reached Ironlock Prison and joined Sally and Antoine inside it.