See inside Eagle's Nest, the 42-acre New York Vanderbilt estate where a Gilded Age heir built his sprawling mansion

The entrance to Eagle's Nest.

Gabbi Shaw/Business Insider The Suffolk County Vanderbilt Museum is a must-see for any "Gilded Age" fan.

The museum was once the estate of William K.

Vanderbilt II, the son of William and Alva Vanderbilt.

Alva is the inspiration behind Bertha Russell, who is played by Carrie Coon on the show.

Can you hear "The Last Great American Dynasty" playing in the distance? There are many historical mansions on Long Island , but only one was once owned by the legendary Vanderbilt family.

The 42-acre estate of William Kissam Vanderbilt II, which included his summer "cottage" of Eagle's Nest, is now a museum that's open to the public.

Eagle's Nest was first built in 1910 as a small cottage, but as William II spent more time there, it expanded until 1936, when a full redesign was finished: It had become a 24-room Spanish Revival mansion.

William II spent time at Eagle's Nest until his death in 1944.

His will stipulated that upon his wife Rosamund's death, the estate would be left to Suffolk County and become a museum, which it did after her death in 1947.

The Vanderbilts are one of the best-known (and richest) families in American history — so much so that Bertha Russell, the main character on HBO's " The Gilded Age ," is based on Alva Vanderbilt, William II's mother.

In fact, a major plot line in season three is based on William II's sister, Consuelo Vanderbilt, marrying the Duke of Marlborough in 1895.

As a fan of " The Gilded Age ," I knew I had to check out Eagle's Nest — even if Larry Russell isn't really based on William II, I still needed to see the real mansion that his character might live in, so I visited in July 2025.

The museum is open every day except Monday, and tours of the mansion are offered every day.