The Flipside is my nickname for the set of new areas that have been created. They are under the existing area and take much the same format as the upper World. The layout is as follows:
To the far north is the "medieval" area, parallelling the "mechanical" area.
To the far east is the "temple" area, parallelling the "ruins" area.
To the far west is the "colony" area, parallelling the "village" area.
To the far south is the "islands" area, parallelling the "caves" area.
To the northeast is the "desert" area, parallelling the "plains" area.
To the northwest is the "tower" area, parallelling the "hole" area.
To the southeast is the "castle" area, parallelling the "mansion" area.
To the southwest is the "demonic" area, parallelling the "sanctuary" area.
The middle of this area exists but is not accessible. As such, users can walk right over it as if it is an empty space.
Monsters in the Flipside are more powerful than any up top. The area is accessible through doors, one in each up-top area, but they are not open yet: as such it is impossible to access the Flipside at this time.
We'll go there later.
Comment if you have questions (as is the case with all these info-posts).