It appears on Auradon's map. It is depicted as a big castle on a Hill, with one great tower, two courtyards and a garden.
The Isle of the Lost describes it:
But right in the center was the grandest castle in all of Auradon, with lavish turrets and balconies, its highest towers flying the proud blue-and-gold banner of the good old USA. Inside the magnificent building were many ballrooms, great rooms and state rooms, a formal dining room that could seat hundreds, where everyone was made to feel like a pampered guest, and a wondrous library that held all the books that were ever written.
Ben's room is a large comfortable room. Its a mix between modern and old styles. It has two entrances (from a hallway and a balcony), a fireplace, a fourposter bed and a table football. This room has a great view to the Island of the Lost
The tower is where Beast placed Maurice when he caught him trespassing. When Belle traded herself as prisoner, Lumeiere advised Beast to "offer her a more comfortable room" rather than keep her in the tower as well.