[shhsshs]

The project has data about every location (doors, chests, etc.) and the conditions that must be met to allow access to those locations - for example [1]. From there the randomizer shuffles various entrances/exits and item locations around using rules that are mostly guaranteed to keep the game beatable.

[1] https://github.com/OoTRandomizer/OoT-Randomizer/blob/d1bb6c2...