Theosophus

Underground City

Theosophus, an entire underground “city” that is the size of the largest country above ground.

The original purpose of this underground structure would have been to shelter as many civilians as possible were a war to break out between countries. This happened before the first World War, the panic taking over most of the country.
After years of building the underground city and storing goods, decades went by without any need for it so it was mostly left untouched until Nexus uncovered it in some files that were long put away.
Nexus decided to clean the place up and reinforce some of the buildings that were built at the time to handle the people that would later be put there to live.

It was only then that they decided the underground city to be a holding place for their “failed experiments” when they got to be too many. Nexus didn’t have anywhere to keep them and they could not kill them because of the valuable information they could provide as live organisms.

Theosophus contains every single live experiment from Nexus, both those made of flesh and those that are not. These experiments border on mostly humanoid creatures, some of which are much too large to be released into the world. Others working vastly different than human beings or the original species they were based off of; these creatures need special attention and care which the world above cannot provide so they are confined.

Because Nexus plans on introducing these beings into the modern world above ground, there are humans who live in Theosophus, these people are mostly comprised of those who have no purpose in life and signed up to be part of Nexus’ experimentation. Some, if not all, are also currently being worked on and have some resemblance to the creatures who have fully turned into less-than-human things. However, these people are more human than monsters, usually only certain aspects of them looking different before the reconstruction stopped.

Theosophy; an approach that emphasized experimentation as a means of learning about the "Unseen Universe".