Anima: The Masquerade
The Machines are mysterious masses of metal and magic. Their true nature is unknown, though they are thought to sustain the the land mass they support by providing it with clean water, fresh air, and other necessities. While there are only three known machines, only one of which is inhabited by any significant human life, it is unknown if there are more of these machines in existence.
At least some of the machines, both of which were visited, contain a complex portal network underneath the ocean. The sheer number of knobs which appear to be used as a dialing system has its implications as well.
Ronald, or The Guardian, is suspected to be directly tied to the machine. Even after being questions, it appears even the guardian himself is uncertain why the machines exist or how they came to be.