The Overgrown City is an obscure, deep-in area reachable from the Industrial Maze, and thus, indirectly, from the Forest Pier.
The Overgrown City resembles just that, a city in which some disaster occurred, that has long since been abandoned and mostly reclaimed by nature. The city is devoid of life, except for a few non-NPC creatures that are only debatably alive at all. The City can be divided into three rough sections. For unknown reasons, you are incapable of using the Bat Effect while in this area.
Entrance
The City can be reached from the Industrial Maze's Garden area, via a door just above the garden itself. After traversing a short passage fraught with amber light, enormous plants, and a strange, mechanical being, you will exit into what appears to have once been someone's back yard, via a manhole. Following the linear path from here will take you into the main part of the Overgrown City itself.
Main Area
This area is extremely tall, and quite wide as well (though going too far in either direction will smack you with a dead end in the form of traffic cones). Throughout the area you will occasionally find what look to be enormous lotus petals, these vaguely resemble Steve "Leif" Kareha, one of the most obscure NPCs from the original Yume Nikki.
You begin at the top of the area, and travel down relatively linearly, eventually the BGM will change to a loud, melancholy piano riff, and you will be in "the bottom" of the city proper. Going east from here, you will encounter another garden not dissimilar to the one found in the Industrial Maze, here, you will find a strange creature composed of orange rock and traffic cones cowing under a disused overpass bridge, possibly dead. Going further east still, you will run into a massive creature with what appears to be a ball of scrap iron for a head, bound up in what looks like an enormous straightjacket. If we allow ourselves a moment of whimsy, perhaps this is what caused the disaster here in the first place.
Going yet further east will cause the BGM to change again, and put you on the path to the Blue Room.
The Aquarium
This building--the only one in the entire city that can be entered--is found on the eastmost edge of the map. Currently, there is very little here but a dark blue glass wall. What purpose this may serve eventually is unknown.
