This question is inspired by Who was dreaming when and whose mind was being projected?, where the infographic shows very well in which mind each dream level takes place, except for the Limbo:
So let's review, what is Limbo?
The top answer on this question provides the movie dialogue that explains it:
ARIADNE Limbo? ARTHUR Unconstructed dream space. ARIADNE What's down there? ARTHUR Raw, infinite subconscious. Nothing there but what was left behind by anyone on the team who's been trapped there before. On this team... just Cobb.
That definition is really vague and does not really provide an answer to where the Limbo takes place, i.e. in which subconsciousness. As we know, usually someone has to sleep and dream the world so the others can link in.
I think it can be compared to hosting a dedicated server for a game. One of the players has to "host" (dream) the world on his "PC" (mind) for the others to be able connect to it. He then is able to control the environment.
Apparently Limbo happens in the subconscious, so the "player" is not able to actively control the environment. Still leaves the question:
In which subconscious does the limbo happen? How is that decided and who is able to control this world?
I would expect the person dying to fall down into their own sub-conscience. However Cobb and Saito are able to meet there, so that cannot be true.