We wanted to show Ukkon's fortress from early on in the development. Since he is the mastermind behind the Locust creatures we also wanted to connect him to Imulsion, which he is using for his experiments.
We did some early explorations, with walkways of a giant Imulsion refinery. A lot changed over time, but the idea of the platform suspended over Imulsion below remained, since it worked really well for the narrative, camera and gameplay.