Gralea

Gralea is the capital of the Empire of Niflheim in Final Fantasy XV. It is located deep in the imperial heartland, and Prince Noctis's mission is to infiltrate it to take back the Crystal of Lucis. Gralea is the empire's seat of power and where the magitek laboratory Zegnautus Keep is also located, high up in the sky.

Story
Prince Noctis is on a mission to recover Lucis's stolen Crystal, which he believes he been taken to the imperial capital. Daylight is vanishing from the world and more and more daemons appear all around the world. Noctis hopes he can save the world with the light of the Crystal as he now has the Ring of the Lucii needed to command the Crystal's power.

Noctis and his friends ride a train driven by Biggs and Wedge into Gralea, but the train is halted by daemons. Noctis drives the Regalia into the city until it is damaged and they abandoned the wrecked car onto the train tracks. Noctis becomes separated from his friends and must look for a way into the imperial magitek lab alone. The city streets are empty and the only inhabitants he finds are daemons.

Gralea has been ravaged by a "vanishing disease" and its citizens have been turned into daemons. A state of emergency has been called with radio broadcasts asking everyone to stay indoors until it has been resolved. When Noctis makes his way to Zegnautus Keep he finds its magitek troopers have gone rogue and even the Emperor has turned into a daemon. A radio transmission Ignis Scientia and Gladiolus Amicitia can listen to on their way to reunite with Noctis implies everyone in town has already become a daemon. After Noctis finds the Crystal and disappears inside it, his friends escape Gralea back to Lucis, and the world is overtaken by daemons.