Cerulea is the planet on which the Big Blue is located. Cerulea is mostly covered in oceans, with many hundreds of islands and the occasional continental landmass. Its climate is much the same as Earth's is, though a little bit more humid and tropical.
However, unlike Earth, Cerulea is home to a mysterious kind of energy known as Change, which has the ability to mutate organic matter, power technologies and bend reality. The closest Terran phenomenon is nuclear radiation, but tampering with Change leads to results far beyond what would be thought possible through conventional science. The surface of Cerulea's oceans are dotted with Unstable Portals that bring people, ships and technology from other worlds, including Earth and the Korbak World.
Cerulea's ecosystems differ from Earth's: there are many fewer trees and shrubs, as dry land less common, although its underwater flora and fauna are much more diverse and abundant. Notable biomes include coral reefs, mangrove forests, giant kelp forests, fields of volcanic hydrothermal vents, caustic brine pools and more. Cerulea has not been subject to the pollution and stress of an industrial revolution like Earth has, and so its ecology is stable and not at risk of irreversible harm.