It is, as the name implies, both a carnival and a circus. It exists outside of our plane of existance, but can be accessed by individuals who accidently wander over to one of the portals hidden by Splendor Man in the form of his flyers, which only work for a few days.
It is described as very large and beautiful, but photography is not allowed, because all images of The Circus Carnival (photographic, hand drawn, digital, etc) fade away until they are blank.
The Circus Carnival changes it's attractions and shows based on whoever enters into it. (EX: If someone is afraid of clowns, no clowns will appear.)
The only problem is that Splendor Man forgot to make a way to leave without his assistance, making it hard to get out as Splendor Man has to focus on opening a portal out, which is very hard to do and requires a lot of energy. This sometimes leads to problems when Splendy is low on energy while someone wants to leave, and has led to severe misunderstandings in the past.