The Overworld is for level 100 and down because you can battle starter mobs like rats and crows but also high level mobs like zombies.
The underworld is a place where you can go to get to higher level monsters than the ones you came from if you want a bit more of a challenge, like if you master crows then you can go to wolves.
|Vampire Dungeon Level 1|
|Vampire Dungeon Level 2|
(NOTE: MORE MAPS COMING SOON!!)