The Lost Shinjuku is the fifth stratum of Etrian Odyssey.
This lost city of the old has been taken away by the nature. Its completely abandoned, and now monsters roam away freely on it. It also has very advanced technology, way more than the one you have back in Etria. As you explore it, you find the reasons of its destruction, the true nature of the labyrinth, and even the mastermind behind the events which took place.
It is home of some of the most powerful creatures of the labyrinth.