I visited an abandoned castle hidden on a small island in New York that's slowly crumbling away, and it was hauntingly beautiful

• The abandoned Bannerman Castle sits on Pollepel Island in New York's Hudson River.
• Once a fortress for weapons, the castle is only accessible by private boat.

Sitting on Pollepel Island in New York's Hudson River is a stunning piece of history that's slowly crumbling away.

Bannerman Castle was a fortress for weapons in the early 20th century built by Francis Bannerman, a Scottish arms trader, The New York Times reported.

Following an explosion of gunpowder in the building, the castle was abandoned in the 1950s, according to the same source. In the early 1990s, the Bannerman Castle Trust led efforts to restore the castle and island to make it safe for the public to visit. It's been accessible since 2004, and since 2020, it's been open for tours.

We got a private tour of the island in 2019 — before tours were available to the public. Take a look at Pollepel Island's decaying castle that's being taken over by nature.

Welcome to Bannerman Castle, an abandoned structure in New York's Hudson River that I visited in 2019. Today, you can reserve tours on the Bannerman Castle website.

A view of Bannerman Castle from the Hudson River.      Joey Hadden/Insider

Source: Bannerman Castle Trust

Bannerman Castle is on Pollepel Island, which is about 60 miles north of New York City.

Pollepel Island is in the Hudson River, north of Manhattan.      Google Maps

The abandoned castle is visible from the Metro-North Railroad's Hudson train line.

Manitou station, the closest train station to Bannerman Castle, is on Metro-North's Hudson line.      Joey Hadden/Insider

To get to the castle, I took a Lyft from the Manitou train station to Donahue Memorial Park in the town of Cornwall, New York.

A view of the Hudson River from Donahue Memorial Park.      Joey Hadden/Insider

The park sits on the west side of the Hudson River. There, I met up with guides from the Bannerman Castle Trust, the group that oversees the preservation and maintenance of the castle.

The picnic area at Donahue Memorial Park in Cornwall, New York.      Joey Hadden/Insider

A boat waited at the park's public dock.

A work boat at the Cornwall public dock.      Joey Hadden/Insider

I crammed into the boat with two guides and a handful of volunteer gardeners who do landscaping work on Pollepel Island.

A work boat at the Cornwall public dock.      Joey Hadden/Insider

It took less than 20 minutes to get to the castle. From the dock, I thought its beautiful, sturdy-looking walls made the building appear almost functional.

The north gate of Bannerman Castle on Pollepel Island.      Joey Hadden/Insider

But my guide told me that I absolutely could not go inside — it's not safe.

A close-up of a turret on Bannerman Castle's north gate.      Joey Hadden/Insider

From the dock, we climbed 72 stairs to reach the island.

There are 72 stairs from the dock to Pollepel Island.      Joey Hadden/Insider

Closer up, I understood why it's not safe to enter the castle. My guide explained that the towers of the castle require external beams for support.

A view of Bannerman Castle from the north trail of Pollepel Island.      Joey Hadden/Insider

The braces are made of steel. Each individual section weighs 250 pounds.

The remaining wall of Bannerman Castle's tower.      Joey Hadden/Insider

But even with this support, there's still a risk that the walls could fall.

Bannerman Castle's remaining tower wall and a warehouse wall.      Joey Hadden/Insider

So all visitors must stay at least 100 feet away from the castle. Observation decks are set up around the castle at picturesque vantage points.

The north trail on Pollepel Island.      Joey Hadden/Insider

A history of accidental explosions and weather damage at Bannerman Castle have left it in this decrepit state.

A warehouse wall (left) and a tower wall (right) held up by steel braces.      Joey Hadden/Insider

Francis Bannerman VI, an arms dealer who lived in Brooklyn, bought Pollepel Island in 1900. He wanted a place outside the city to store an arsenal of munitions, according to the New York Times, so he built the fortress and an accompanying harbor.

Pollepel Island.      National Archives and Records Administration

Source: The New York Times

Bannerman's sons took over the business when he died in 1918. But in 1920, a room full of gun powder exploded, shattering some of the windows, according to the same source.

A close-up of a Bannerman Castle wall shows where windows used to be.      Joey Hadden/Insider

Source: The New York Times

Forty-seven years later, the Bannerman family sold the island to New York State, according to the New York Times. It eventually became part of the Hudson Highlands State Park Preserve.

A view of Bannerman Castle's tower from the observation deck.      Joey Hadden/Insider

Sources: Hudson Highlands State Park Preserve, The New York Times, Business Insider

In 1969, a fire destroyed much of the castle, leaving it unusable.

A view of Bannerman Castle and remnants of its harbor.      Joey Hadden/Insider

Source: The New York Times

After that, Pollepel Island was deemed unsafe and declared off-limits by the State of New York.

A view of Bannerman Castle from the Hudson River.      Joey Hadden/Insider

Source: The New York Times

But in 1992, Neil Caplan, a resident of nearby Beacon, New York, formed the Bannerman Castle Trust. The group raised money to restore the island; Caplan is its executive director.

A view of Bannerman Castle walls from the Hudson River.      Joey Hadden/Insider

Source: The New York Times, Bannerman Castle Trust, Business Insider

The Trust teamed up with New York's Office of Parks, Recreation, and Historic Preservation to open the island to the public in 2004.

Bannerman Castle's tower as viewed from an observation deck.      Joey Hadden/Insider

Source: The New York Times, Bannerman Castle Trust

Today, it serves as a theater, museum, and historical site.

A stage set up in front of Bannerman Castle's visitor center.      Joey Hadden/Insider

Source: Bannerman Castle Trust

Although the main castle is inaccessible ...

A close-up of Bannerman Castle as seen from a boat on the Hudson River.      Joey Hadden/Insider

Source: Bannerman Castle Trust

... the Trust has stabilized the structure that served as the Bannerman family residence. That's now the island's visitor center.

The Bannerman family residence is intact and safe to enter.      Joey Hadden/Insider

The facade of the building also serves as the backdrop for the theater's stage.

The Bannerman family residence.      Joey Hadden/Business Insider

Inside, visitors can find information about the island's past.

The entrance to the Bannerman Castle visitor center.      Joey Hadden/Insider

Modest exhibits explain the site's history and the construction of the castle.

Historical information in the Bannerman Castle visitor center.      Joey Hadden/Business Insider

Drawings and documents about the castle and the Bannerman family are framed on the building's distressed walls.

Historical information in the Bannerman Castle visitor center.      Joey Hadden/Insider

Visitors can also see preserved fixtures from the castle, like this bathtub.

A bathtub that was saved from Bannerman Castle.      Joey Hadden/Insider

The center also has a gift shop that sells art and T-shirts.

The gift shop in Bannerman Castle's visitor center.      Joey Hadden/Insider

Although the trust has restored parts of the castle since the '90s, the weather has still taken a toll on the structure in recent decades.

An arch beneath a section of Bannerman Castle's grand staircase.      Joey Hadden/Insider

Much of the castle's shell collapsed one night in December 2009.

A view of Bannerman Castle from the Hudson River.      Joey Hadden/Insider

Source: The New York Times

Then more walls fell just a month later, during a January storm in 2010.

A view of Bannerman Castle from the Hudson River.      Joey Hadden/Insider

Source: Bannerman Castle

Wear and tear from the elements is visible on the walls that still stand.

A close-up of the remaining walls of Bannerman Castle's tower.      Joey Hadden/Insider

On the way back from the castle, the boat took a spin around the island's perimeter.

The work boat travels back to land from Bannerman Castle.      Joey Hadden/Insider

From the water, we caught glimpses of other pieces of the abandoned fortress ...

Remnants of Bannerman Castle's harbor.      Joey Hadden/Business Insider

... including its deteriorated harbor.

Remnants of Bannerman Castle's harbor.      Joey Hadden/Insider

From afar, it was especially clear that nature has already taken over many parts of this mysterious piece of history on the Hudson River.

A view of the castle from the Hudson River.      Joey Hadden/Business Insider