The Slaughter Swamp is a paranormal wetland region found on the outskirts of Gotham. It is best known for its role in the birth of Solomon Grundy, with its waters and plant-life bonding to Grundy's corpse to resurrect him as an undead behemoth.
Earth Two (Golden Age)
In 1894, a wealthy merchant named Cyrus Gold was murdered and dumped in the Slaughter Swamps outside of Gotham. The corpse bonded with the fauna of the paranormal swamp and became re-animated as an amnesiac beast of half-corpse and half-plant.
Now called Solomon Grundy, in 1944 the zombie would become an enemy of the Gotham City vigilante Alan Scott AKA The Green Lantern.
Appearances in Other Media
The Slaughter Swamps are used as the base of operation for the Legion of Doom, with their base, "The Hall of Doom" being found under the water's surface.
Adaptions of the Legion would often move the Hall of Doom to the swamps of Louisiana and/or within a marsh region referred to as, "The Suicide Swamps" which could be an alternate moniker for the Slaughter Swamps, a region in the Louisiana parish, or a different swamp all-together.
In Justice League Unlimited, the swamps are unnamed and marked by a wooden sign decorated with skulls as a warning. In the 1920s, gangster Cyrus Gold was dumped in the swamp by rival gangsters after they murdered him with Tommy-guns.
The Slaughter Swamps are mentioned as part of Solomon Grundy's origin story.
The Slaughter Swamps appear as a stage to be fought in within this video-game. It is shown to have several wooden homes in it and crocodilians which the locals hunt.
In this TV series, the Slaughter Swamps are where Hugo Strange dumps the waste from his mad science experiments. So when mobster Butch Gilzean (born Cyrus Gold) was dumped into the swamps, he was resurrected as an amnesiac undead being with an enhanced healing-factor.