4) Arkham, Ace Chemicals And Belle Reve
A number of locations that will be familiar to fans of the Joker and Suicide Squad make cameos in the film. First of all, you can’t have Task Force X without Belle Reve Penitentiary, where most of the team are incarcerated. The facility previously appeared in live-action on Smallville and Arrow.
But Harley Quinn, of course, is tied to Arkham Asylum instead, the madhouse where most of Batman’s enemies are held (and frequently break out of). It appears in all its gothic glory here during Harley’s flashbacks and can also currently be seen in FOX’s Gotham.
Finally, the location of the scene with Joker and Harley and the vats of chemicals isn’t named on screen but one of the vats is labelled ‘Ace Chemicals’ – where Joker’s story began, according to The Killing Joke. The plant was previously alluded to in BvS as well.