How's this look:

Enemies not included in preview, I'm at school right now or I'd put in sprites where they'll be. This is overworld, the player starts at the bottom left corner of the bottom right screen. The chest contains Roc's Feather. This is mostly me messing with the editor.
The idea behind the deep water in the bottom left corner is that it leads to the final boss. The player must return here through all of the overworld after acquiring the Mermaid Suit from the final dungeon.
The first dungeon is down those stairs.
Also, do any dungeons have those breakable floors that turn into holes? I can't seem to find them.