In the US, here are some of it from Conde Nast Traveler.
1) Biltmore Estate, NC.
Biltmore may lack the castle moniker, but with that glorious French Renaissance façade—and at almost 200,000 square feet—it certainly fits the bill.
Built by George Washington Vanderbilt II between 1889 and 1895, the estate wasn’t even intended to function as the main residence, but merely as a summer home. (The other Vanderbilts at the time chose to erect more "modest" summer homes in Newport, RI like The Breakers.)
The estate is still owned by the Vanderbilts—making it the largest privately owned home in the country—but a pedigree is no longer required to visit. In addition to self-guided tours, visitors can stay on-site (just not in the estate) and explore the Downton Abbey costume exhibit.
2) Boldt Castle, NY
Like Biltmore, Boldt Castle was meant to be a summer home around the turn of the 20th century. Unlike Biltmore, it was never lived in: Millionaire hotel developer George C. Boldt commissioned the 120-room estate (on Heart Island, no less) as a display of love to his wife. Sadly, his wife passed away suddenly just months before completion. Boldt abandoned the project, leaving it to fall into disrepair.
Luckily, the Thousand Islands Bridge Authority stepped in in 1977 to restore and preserve the property. Today, it offers self-guided tours, and as of this May, guests can now view the restored kitchen and servants' dining rooms. (© National Geographic Image Collection / Alamy)
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