Necessarius Underground Labyrinth

Necessarius Underground Labyrinth (ネセサリウスの地下鉄迷宮) refers to the complex arrangement of underground tunnels found in London used and maintained by Necessarius. It was used by Necessarius to test new recruits before becoming official members, notably the Amakusa Christians who passed the actual physical test instead of the "virtual" one that was prepared for them.

By late October of the current year of the timeline, the labyrinth has been decomissioned for being too dangerous, becoming off limits as people kept dying in it, though periodic tests are apparently still carried out.

Principles
The labyrinth are made up of unused tunnels and stations, and is part of the London Undergound. This is backed up by the entrances that are connected with the labyrinth such as the subway entrance that Bayloupe and Itsuwa came in, an entrance in the station at Soho for the "virtual test", and the F2 entrance at Lambeth Station, with it being protected by shutters that need a code to open. In fact, several tunnels connect to that station, though they are all abandoned and the rails ahve been partially removed. In spite of this, the tunnels in the labyrinth have fluorescent lights that can be turned off when the test begins. One of the tunnels lead to a station's lost article storage room through a special mechanism allowing for it to be connected to the labyrinth. This is also where items people had left behind or dropped are gathered, and apparently where the results of tests in the labyrinth are kept.

The tunnels are filled traps, danger zones, as well as routes for the power supply.

Traps
As Necessarius uses the labyrinth, it was filled with countless varieties of traps, both magic and non-magic. This combination allows a greater challenge for magicians who enter the labyrinth as the risk of overlooking something rises.

The labyrinth itself is a large spiritual item, and was made so that the victims that succumbed to the traps would be automatically transported out and any items were dropped there were separated and collected. One trap is the labyrinth being able to magically switch the paths, like a tunnel becoming curved even though the route was supposed to be straight. Other known traps were the transforming coprse wax and the water wheel.