Dungen Gunden is the city located outside of Erwin's fortress. This is a major part of the game, as you are now infiltrating the major bulk of Erwin's Fortress.

Nefarious Scheme 57

"Orson, what's with the weather? This looks like the end of the world!"
— Pac-Man

After going through, and surviving, Erwin's Fortress, Pac-Man now has to go around the major bulk of the Fortress in order to get to the syphon hidden deep in Dungen Gunden. Along the way, Erwin communicates to you, sending out various empty threats and revealing the greater part of his scheme to you. As you make your way around the outer wall and into the city itself, you notice that the weather has changed, an obvious indication of what is to come should the Spectral Realm collapse. The skies above this town are a gray-green, the could resembling the more-common thundercloud.