Board Thread:General Discussion/@comment-26340222-20160312083256/@comment-24674051-20160314161742

I'm not so sure about that. Based on last nights episode, ALL of the graves are in a common cemetary, which is right outside, or maybe a part, of UnderBrooke. Snow was commenting that all the graves she was seeing were people from her  kingdom that she was responsible for protecting (and failed miserably, obviously). Also, Herc's grave was in that very same graveyard.

So I'm guessing that there is only one Underworld, thought there certainly seem to be different sections to it. And by Hades admission, there is some yet unknown reason why UnderBrooke resembles Storybrooke. (Well, unknown to us, though Hades knows and just isn't telling yet).