"Bingo. The final layer has appeared," saying so; he then got to work while whistling a carefree tune.
Floating in front of an enormous circular stone door embossed with numerous glittering runic arrays, Prometheus extended both of his hands and typed on its surface with his fingers.
His dirty, boney fingers danced at blurring speeds as lines and mysterious characters formed of magic power formed on the air in front of him and flew towards the various arrays on the stone door.
The moment those characters reached their destined runic array they simply sunk into its surface and merged with it. The array then intermittently blinked with flashing light, a few times, and then disappeared from the stone door.
Essentially, Prometheus was breaking the runic array seals placed on the circular exit door at speeds unseen by the naked eye while replacing them with seals of his own to not trigger any alarms.