Undercity (Judge Dredd)

The Undercity is a part of the fictional universe featured in the Judge Dredd series that appears in the UK comic book 2000 AD.

In the comic strip, the cities of the Eastern Seaboard of the United States had become so polluted that by the end of the twenty-first century they were simply sealed over with concrete, and a new city was built on top. This city was to be named Mega-City One, whilst the remains of the old city below became known as "the Undercity". (Tempest established that a few significant buildings were moved to the Mega-City for the tourists)

The only Judges who operate in the Undercity are the few who have taken the long walk and elected to serve in the Undercity.

Hondo City (future Japan) also has an Undercity, shown in the second Shimura storyline.

The Undercity is inhabited by various mutants and criminals (or perps as they are known in the comic), and has featured in several Judge Dredd stories. These always involve confrontations with the inhabitants (often blind and sometimes mutated), as well as travel to some remarkably well-preserved locations that would still be familiar to present-day inhabitants of the region.

Dredd and a small band of rebel Judges (along with undercity denizen Fergee) lead the resistance against the insane Judge Cal;

In the aftermath of the Apocalypse War, while the city is getting back on its feet, a crack in Norman Pitlik block opens. This cleft extends deep below the city allowing a number of strange creatures to the surface – werewolves.

The judges manage to defeat them but it turns out one of the werewolves is Judge Bram, who had taken the Long Walk. An infected Judge Korkoran also transformed before being subdued by a headbutt from Dredd. With these subjects to work on Tech Judge Cassidy discovers a radioactive compound that is causing the changes, which he names Cassidium.

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Wikipedia