Lazlayon, also known as the Gilded Bog, is the secret military base used by Nikolai Lantsov to develop weapons and combat vehicles. To the public, it is the home of Count Kirigin, a wealthy young man employed by Nikolai to fool Ravka's enemies.
The mansion, while named Lazlayon the Gilded Hallow, has so much fog that it was nicknamed the Gilded Bog.
King of Scars
Nikolai arrives at Lazlayon to observe David and Nadia's progress on his submarines. The Kerch discover Nikolai's projects there, and come to Ravka to investigate. Isaak, posing as Nikolai, stands in while the Grisha Triumvirate stage an elaborate explosion.
The facility has different sections, including ones for Materialki, Corporalki, and Etherealki. The main project being developed there is Nikolai's submarines, which he plans to use in nautical battles with Fjerda and the Shu Han.