I have read in some guide books about a small separate building that requires room keys to enter. Has anyone stayed in this building and how are the rooms? It seems that this location wouldn't be as nice as in the main building. Can you request not to have these rooms?
Could it be the garden suites that you read about? These suites are located in the garden area (hence the name!). This is a specific category of room (and very expensive), so you wouldn't get these unless you book them (I would imagine free upgrades to these are rare indeed). This is the only room type that I can think of that is somewhat separate, but maybe someone else has some ideas.