The familiar architecture takes a step to the right as they get closer, revealing it to be more of a modern fortress-home built on the bones of a roman villa, from the building materials to small touches to the architecture which make it just a hair anachronistic, even here where the attempt at mimicry is strongest.
There are glass doors inside the archways leading onto the terrace they're now on, the rooms inside hidden by curtains pulled across them. Ganauche doesn't lead them towards any of those, instead taking them to the right along the terrace to a more discrete door set into the outer wall, where it meets the east tower there.
Inside is a short hall. They hang a quick right into the tower rather than going further into the building, and climb the stairs there, exiting the tower one floor up.
A description of the labyrinthine route the group takes from this point to Alex's grandfather's study would be long and convoluted. Suffice to say they pass through several open courtyards, walk down many more halls, and take at least three more staircases, two down and one up. The decor is expensive-looking if unfamiliar, much of it pretty clearly antique or made to look that way, and the art, which fills the halls tastefully throughout - paintings, tapestries, statuary, vases, and more - ranges from exquisite to bland. They pass many servants doing basic maintenance and going this way and that through the halls, along with well-dressed men and women on other business, all of whom nod respectfully to Alex, some of whom nod respectfully to Ganauche, and many of whom eye Leo curiously as they pass.
Entering the study itself requires going through the Don's sitting room. Ganauche lets them through the glass doors without any comment from the guard there, and then knocks on the door to the study.