What Are Sub-Layers?
Sub-layers are locations that usually add more detail to an existing level. There are two types of sub-layers — "sub-levels" and "rooms". Sub-levels are levels that are related to their parent level, but are still their own distinct level. Rooms are locations that are too small to be considered their own level. Usually, they are places in an existing level, but that is not always the case.
Sub-Levels Mainlist
Sub-levels are intended to add lore, or "depth" to an already written level. Think of them as spin-offs of the level they can be found in, levels within the level, or a level between two other levels. A sub-level is usually smaller, albeit more detailed — but not always. A level can have as many sub-levels as one can imagine, as long as they maintain the loose theme of their parent level.