IMVU World.

IMVU Dimension: A 3D/CGI world that is based around the chat program IMVU, the avatars or characters that are created on the program can walk around in the city and various locations and talk to others there, and people who enter this dimension can be transformed into their avatar/character creation  (with a little bit of MC on the side if the creation they have has an established personality both in and out of this world) and explore the locations as a whole.  You'll often find the animated versions of Nathan and his friends in this world and they're all in the style of the program's avatars,  but fully animated and alive and they can do all sorts of things.

The way to get to this dimension and all the various different 'room-realms' is via a Stargate-like portal or a vortex or teleportation circle,  when you are teleported there in either one of the aforementioned ways you are introduced to some of the residents of this dimension. There are aspects of it which involve crossovers with other characters as well.  There is always something supernatural or paranormal going on in this dimension and Mel the koala-girl is the resident paranormal investigator who goes around solving them.