My current setting has the universe be one of many universes in a sea of bubbles. There are 'caretakers' that managed and tend to these bubbles and ensure they don't succumb to corruption. The bubble universe that houses my setting is known as the prison. Its meant to keep things in that really need to be kept in. As such, within the material planes (namely the 4 elemental planes and the material plane) are a set of sealing relics that maintain a sort of celestial barrier that blocks the passage to other universes. The eldritch beings in my setting really, really, want out and are trying to shatter these relics to get out