The city of fairies was being remade as the city of the dead. Most of the Undeads were left behind in the floating city to prepare the city as a fortress.
The formations that were left behind by the fairies were mostly destroyed by Karyk when he came to the city. During his onslaught, most of the protective mechanisms had been destroyed.
Some of those mechanisms were responsible for even keeping the city hidden from the world, being extremely important.
Karyk left behind the Undead Fairy Lord and the other fairies who knew better about such things.
Even though they were undead, they could still access the memories that Karyk wanted them to access. As for the memories that he didn't want them to explore, it was kept sealed away from them.
The Fairy Lord started working on the formation, not only repairing them but even strengthening them even further.
