The Yggdrasil Labyrinth is the name of the dungeon that is explored in each game. The majority of gameplay is conducted here within the labyrinth, where you explore the unknown and fight monsters.
Games
Etrian Odyssey I
On its first incarnation, the labyrinth emerged on the vicinity of Etria, bringing out explorers of every place of the world, in order to brave its depths.
Etrian Odyssey II
This labyrinth takes place inHigh Lagaard. The labyrinth begins through the forest around its respected Yggdrasil Tree, going higher into the flying fortress that once was home to people of the city.
Etrian Odyssey III
The third incarnation of the labyrinth is very different from the previous ones, leading deep into the sea, to the Deep City, a part of the city know as Armoroad that was once lost during a calamity of the past.
Etrian Odyssey IV
The labyrinth isn't present in the fourth game of the series in its traditional form. Instead, the exploration takes place in smaller dungeons known as Mazes. They are connected by big, wide open areas explored using an airship.
Etrian Odyssey V
The fifth game's labyrinth is located at the Yggdrasil Tree in Arcania, near the city of Iorys.
Strata
The labyrinth is split into various zones known as Strata (singular Stratum, plural Strata), divided into a number of floors (usually 5). Each stratum has its own type of environment and monsters that inhabit it. The background music played while exploring also changes between strata. Also, each stratum is protected by a powerful boss monster.