An overgrown and in many places overflooded factory that was once used for constructing massive tools of war. It's now used for shelter by animals and as a spot for plant growth, but many rooms and built-in contraptions still heave with its fading legacy.
Since it's been around for so long, it has many plant and animal species native to its area. There's even a kind of bacteria that feeds off of its rust, as well as various kinds of fish and crustaceans able to live in its polluted waters.