The NightWing fortress, which was made from tunnels of volcanic rock, had been the previous home of Queen Battlewinner, Princess Greatness, and around two hundred other NightWings. It was introduced in The Hidden Kingdom and is the main setting of The Dark Secret. Unlike the other palaces and fortresses, the NightWing Fortress cannot be seen on the map of Pyrrhia. Starflight's father, Mastermind, was working on a way to protect the fortress from eruptions until the project to study RainWing venom started. The fortress later exploded from the volcano eruption. Since then, the NightWings have lived in the Rainforest Kingdom. It also is known that this fortress held one of the three dreamvisitors created by Darkstalker, which was found in an abandoned treasure room on a destroyed part of the island by Starflight and Fatespeaker, and was in the possession of a guard who died in a previous eruption.
The NightWings had previously lived on the mainland, but after Darkstalker's attempt to secure the throne, they fled to this island, hoping that it would keep them safe from the animus, not knowing that Clearsight had already put Darkstalker to sleep.
The island was initially host to many plants and animals, but about eleven years before the events of The Dark Secret, the volcano had erupted, removing many of the indigenous lifeforms. The eruption destroyed much of the fortress, including a treasure room that would later be rediscovered by Starflight and Fatespeaker. One of the dreamvisitors created by Darkstalker was sealed within, held by one of two guards who had perished in the room during the eruption.
When the volcano exploded a second time, the fortress was destroyed by lava, forcing the entire NightWing tribe out of their home. With the help of Queen Glory, the NightWings relocated to the rainforest.
Later, in Winter Turning, Icicle flees to the fortress after killing a NightWing guard in the rainforest. Winter, Moon, Kinkajou and Qibli enter the destroyed fortress to search for her, eventually finding her with burns and blisters on her scales. After Icicle threatens them and tried to kill Kinkajou, Queen Glory arrives and knocks her out with a blow dart, arresting her.
The fortress once housed the queen of the NightWings and most of the tribe. Rooms included a huge library full of scrolls, Mastermind's lab where he conducted experiments (such as the prototype for Queen Battlewinner's armor and documenting information on the RainWings and their venom), the Council where Starflight was interrogated in front of his tribe, and dormitories for dragonets. It also included the Throne Room that housed Queen Battlewinner's private chambers, which were only accessible through a secret entrance hidden behind a map of Pyrrhia. She was able to pass orders to Princess Greatness through a screen called the Queen's Eye. The fortress also has dungeons and prisons, some of which were used to hold the captured RainWings.
The NightWing volcano island was accessible from two locations. The first was the animus tunnel created by Stonemover. It led directly from the Rainforest to the volcano island. The second was to fly to it over the sea, and it could be found if a dragon flew north from the Claws of the Clouds Mountains in the Sky Kingdom.