Boldt Castle is a grand castle-like structure located on Heart Island in the Thousand Islands region of the Saint Lawrence River in the United States. It was built by hotel magnate George C. Boldt in 1900 as a tribute to his wife, Louise. However, construction was abruptly stopped after Louise's death, leaving the castle unfinished for over 70 years. In 1977, the Thousand Islands Bridge Authority purchased the property and started restoration work. Today, Boldt Castle is open to visitors and is a popular tourist destination in the area.

The castle features a range of architectural styles, including German Renaissance, French Renaissance, and medieval styles, and it is considered one of the finest examples of American castle architecture. Its grand rooms, towers, and stairways are adorned with intricate details and ornate furnishings. Visitors can explore the castle's many rooms and admire its beautiful gardens and grounds, as well as its stunning views of the river and surrounding islands.

Boldt Castle is a symbol of love and devotion, and it continues to attract visitors from around the world who are drawn to its rich history, stunning architecture, and breathtaking location.