The Yggdrasil Labyrinth is the main dungeon the DS dungeon crawling franchise Etrian Odyssey. The 25 to 30 floor dungeon is the only explorable area in the game and is where most of the game takes place. The Labyrinth is divided into 6 Strata, each with their own unique appearance and creatures.
1st Stratum: Emerald Grove - Floors B1 - B5
A woodland area, like any other. Mostly inhabited by wild rats, rabbits, wild boars and wolves.
2nd Stratum: Primitive Jungle - Floors B6 - B10
A darker jungle area. mostly inhabited by Gels and gorillas. Some tiles have thorny vines littering the ground that are harmful to step on.
3rd Stratum: Azure Rainforest - Floors B11 - B15
Filled with florescent blue trees and plants. Mostly inhabited by ants and sea creatures. Some floors feature pits that drop the party to lower floors.
4th Stratum: Sandy Barrens - Floors B16 - B20
A traditional desert area with shifting sands that behave similarly to conveyor belts.
5th Stratum: Lost Shinjuku - Floors B21 - B25
The lost capital of the humans, and the root of the Yggdrasil Labyrinth.
6th Stratum: Claret Hollows - Floors B26 - B30
A cave-like area with creatures that look suspiciously similar to blood cells. It is also home to the Prime Evil itself.
Etrian Odyssey II: Heroes of Lagaard
Unlike the other games, the Labyrinth in Etrian Odyssey II progresses upwards instead of downwards.
1st Stratum: Ancient Forest - Floors 1 - 5
An old forest with ruins that hints to an earlier civilization. Many woodland creatures reside in these woods.
2nd Stratum: Auburn Thicket - Floors 6 - 10
Fiery woods permanently in the Fall season, with damage tiles spread throughout the area. Pumpkins are known to wander these floors.
3rd Stratum: Frozen Grounds - Floors 11 - 15
A frozen land with filled with heavy snow and slippery ice. Arctic creatures make their home here.
4th Stratum: Petal Bridge - Floors 16 - 20
A garden-like area filled with Sakura trees and floating islands. The party will have to watch out for pitfalls scattered around.
5th Stratum: Heavenly Keep - Floors 21 - 25
The floating castle itself, its golden halls filled with conveyer belts and dangerous creatures.
6th Stratum: Forbidden Woods - Floors 26 - 30
Floating islands scattered around Yggdrasil, it is said to house a creature more dangerous than any other.
Etrian Odyssey III: The Drowned City
In Etrian Odyssey III, most strata only has 4 floors instead of 5.
1st Stratum: Waterfall Wood - Floors B1 - B4
A lush swampland with waterfalls and sticky mud. Wild woodland creatures can be found here.
2nd Stratum: Undersea Grotto - Floors B5 - B8
An undersea area with coral reefs and raging currents. Schools of fish swim these floors, looking for new prey.
3rd Stratum: Molten Caves - Floors B9 - B12
Lava caverns filled with damaging lava tiles and flying dragons. The party can travel on rock rafts to cross lakes of boiling lava.
4th Stratum: Abyssal Shrine - Floors B13 - B16
A shrine previously used by Armoroad, it is now home to creatures that threaten the city itself. Steel gates block the path of both adventurers and beasts.
5th Stratum: Porcelain Forest - Floors B17 - B20
The Royal Forest, with invisible tiles and teleportation gates abound.
6th Stratum: Cyclopean Haunt - Floors B21 - 25
A strange jungle that looks almost alive. It is the only stratum in Etrian Odyssey III to have 5 floors and is home to the Abyssal God himself.
Etrian Odyssey IV: Legends of the Titan
Etrian Odyssey IV features a significantly different Yggdrasil Labyrinth: It's mazes are not directly connected with each other, and most of them only have 3 floors. There also exists smaller caves that are not linked to the main labyrinths at all. However, they are still somewhat connected, and as such, part of Yggdrasil itself.
1st Maze: Lush Woodlands
A natural labyrinth in the Windy Plains, home to dangerous bears and sweet-smelling trees.
2nd Maze: Misty Ravine
Hidden deep in the Scarlet Pillars, the thick mist and unvarying scenery disorient many explorers. Home to the Vessels.
3rd Maze: Golden Lair
Heated streams flow through this humid grotto in the Sacred Mountains. Special scales litter the area, and the Sentinels make their home here.
4th Maze: Echoing Library
A library in the center of the Cloudy Stronghold. It was left by the creators of Yggdrasil, with odd statuary and mechanical guards.
5th Maze: Forbidden Capital
A mysterious research facility deep within Yggdrasil. Yggdrasil's power may sleep here. It is the only maze to have a single floor, but there exist connections to other places...
6th Maze: Hall of Darkness
A large, gloomy library, located in the Cloudy Stronghold away from Yggdrasil. Dangerous creatures inhabit its walls.