From the introduction:
The Inn is a dungeon. It is a campaign setting. It is a town or even just a home for the parties to come back to and visit. It can be and is whatever you need it to be. Literally offering its guests worlds of opportunities.
The Inn is as expansive and expandable as any premade dungeon has ever been and much more than others could have ever hoped to be. It provides your characters a place to grind, explore, call home and anything else you and your party wants it to be in order to do whatever is the most important part for you.
At the Inn there are many thousands of Rooms available. These Rooms can be explored, exploited, conquered and controlled. The backup dungeon master’s campaign setting can even be in a Room, making switching campaigns both easy and part of the story line. The only limits of what possibilities there are, are the limits you set for yourself.