At the (relative) beginning of Thor: Ragnarok, Hela returns to Asgard after a long absence.
Odin expelled her—he mentions that he can’t hold her off any longer. Hela mentions that she was banished. But where to? I don’t recall it being mentioned in the movie.
The obvious answer is to Niflheim, but given that the Marvel universe (and the Marvel Cinematic universe) has altered many things, this isn’t certain.
Where was Hela banished to?