Not a whole lot going on but if you want to explore in-game you can do so by opening the console and type "COC VerySolitude" without the quotes
If you take a door here you will actually be in the original Solitude. If you turn around and go back through that door you remain in regular Solitude. This is intentional as all cell connections are preserved. This could become a Winter season variant, or a Dark world where Thalmor or Vampires took it over years ago, or anything else. Point being its a clean canvas
I preserved ITMs that came with the replication. They aren't what they seem though in this situation and don't matter but you can clean them if you want to. Any texture packs that affect Solitude reflect here as well