Been working on a sewer mod for a couple years now, duplicating and renaming cells to add sewer systems to all the cities. Each cell has to be unique because you can't have sewer door 03 in IC market sewers connect to the south tunnel sometimes and connect to a sewer under Anvil or Skingrad other times, you have to duplicate and rename the entire cell for each location. Everybody knows that - or do we?

Got an idea about adding metal stress sounds to the interiors of spindle towers in Oblivion, and looked it up - there are a total of 10 standard oblivion gates and 90 random gates that appear in different locations, 50 random in each game. Examining the cells in CS I notice there are only a few "rending halls" and "corridors of dark salvation" and so forth. I never counted but "16 planes of Oblivion" would indicate there should be at least 16 unique sets of cells. I understand these are outside the cyrodil world, but how do they re-use interior cells for the different instances of Oblivion?

The doors connecting them use a random teleport list. I don't know how it actually works, but that's how they can reuse a few interiors for all the Oblivion planes' templates. I recall the doors themselves are fixed by the UOP since apparently you can end up losing all possible destinations of a door and get stuck there somehow.