The Circus is a secret facility located in Detroid and controled by ARGUS, where the organization keep prisioner beings not natives from earth or even from the earth dimension. Nicknamed as breachers, the inmates include either supernatural creatures as demons and angels(the Demons Three and an angel from the Bull Host); alien looking lifeforms (as Krakkl); parahumans natives from other dimensions (as Gypsy and Cybernary).
After ARGUS jailed Vibe in the Circus, the young meta caused a break out and several inmates escaped. Some of them,as Lady Quark, returned to their natives realities.
A second break out ocurred when Darkseid daughter, Grail, escaped.
How many inmates still are in the circus is unknown.