Today, Boldt Castle is accessible by ferry, private boat, or by tour boat from Alexandria Bay, New York, Clayton, New York, Gananoque, Ontario, Rockport, Ontario, and Ivy Lea, Ontario.
Most of the grounds and buildings can be explored by the public for a fee.
The boat-owning public may also dock at Heart Island for free.
There is a U.S. Customs and Border Protection office (wood structure manned by single customs officer) on Heart Island, and visitors coming from Canada require appropriate identification, as visiting the island is considered entering the United States.

 As of 2011, most of the rooms on the first floor, and many of the rooms on the second floor of Boldt Castle are furnished, but mostly with modern pieces.
The basement is mostly unfinished, with a pool, bowling lanes, many compartments, and a long passage to the Power House.
Most of the rooms from the second floor to the top floor have been left unfurnished, but there are exhibits in some of these rooms and corridors, showing pictures and artifacts of the Thousand Islands region during the era in which the Boldts lived.
These rooms are also left unfurnished to give the visitor an opportunity to imagine what the castle looked like before modern improvement.
At the edge of the island, a monument stone triumphal arch, originally intended by George Boldt to be the entrance way for boats, has been fully restored.
The bridge connecting the two sides would have been raised and lowered as required.

Two other buildings on the island are the Power House and the Alster Tower; both are open to the public.
The Power House was built to hold a generator to supply the island with power, and now is more of a museum of how electric power was obtained in the early 1900s, as well as a few stories of getting tools and equipment to Heart Island during the castle's construction.
The Alster Tower was purposely constructed with slanting and uneven walls, ceilings, and roofs.

The George C. Boldt Yacht House on nearby Wellesley Island is unique, warranting a visit by means of a shuttle boat connecting it to Heart Island.
It was listed on the National Register of Historic Places in 1978.

The 1969 children's novel Secret Castle by Anne Colver is about the castle and Alexandria Bay.
Today, Boldt Castle is accessible by ferry, private boat, or by tour boat from Alexandria Bay, New York, Clayton, New York, Gananoque, Ontario, Rockport, Ontario, and Ivy Lea, Ontario. Most of the grounds and buildings can be explored by the public for a fee. The boat-owning public may also dock at Heart Island for free. There is a U.S. Customs and Border Protection office (wood structure manned by single customs officer) on Heart Island, and visitors coming from Canada require appropriate identification, as visiting the island is considered entering the United States.
 As of 2011, most of the rooms on the first floor, and many of the rooms on the second floor of Boldt Castle are furnished, but mostly with modern pieces. The basement is mostly unfinished, with a pool, bowling lanes, many compartments, and a long passage to the Power House. Most of the rooms from the second floor to the top floor have been left unfurnished, but there are exhibits in some of these rooms and corridors, showing pictures and artifacts of the Thousand Islands region during the era in which the Boldts lived. These rooms are also left unfurnished to give the visitor an opportunity to imagine what the castle looked like before modern improvement. At the edge of the island, a monument stone triumphal arch, originally intended by George Boldt to be the entrance way for boats, has been fully restored. The bridge connecting the two sides would have been raised and lowered as required.
Two other buildings on the island are the Power House and the Alster Tower; both are open to the public. The Power House was built to hold a generator to supply the island with power, and now is more of a museum of how electric power was obtained in the early 1900s, as well as a few stories of getting tools and equipment to Heart Island during the castle's construction. The Alster Tower was purposely constructed with slanting and uneven walls, ceilings, and roofs.
The George C. Boldt Yacht House on nearby Wellesley Island is unique, warranting a visit by means of a shuttle boat connecting it to Heart Island. It was listed on the National Register of Historic Places in 1978.
The 1969 children's novel Secret Castle by Anne Colver is about the castle and Alexandria Bay.
Boldt Castle