Mystery house

We found this arial view of our neighborhood on a flyer promoting an apartment building currently under construction.
That’s our building, the orangish one in the lower right hand corner. 5 floors with 4 or 5 apartments per floor. Not a huge place, but not small, either.
The building marked with a big yellow question mark, surrounded by its own forested park, is a mystery. It seems way too big to be a private house but there is no sign outside except for a family name on a single mail drop in the wall.
Although there’s a big entrance gate, we never see any traffic going in or out. Once in a while there is a car parked on the horseshoe drive. Maybe someday when I’m feeling extra brave, I’ll stride up and knock on the door to find out what’s up there.