From Creatures Wikia
The default world - which the Emergency Kit and World Switcher use to reset or make a new world - is stored in Eden.sfc, and the current world in World.sfc - although you can also use different files if you're using cheats or the World Switcher. Third-party worlds come with their own sfc files.
Although the file format is not fully understood, openc2e is capable of extracting enough data from an SFC file to enable default worlds (or any without creatures present) to be loaded almost entirely. Its source code contains a Python script for doing this, as well as the C++ code used by the engine itself.