The Thousand Islands International Bridge (French: Pont des Mille-îles) is an American-maintained international bridge system over the Saint Lawrence River connecting northern New York in the United States with southeastern Ontario in Canada. Constructed in 1937, with additions in 1959, the bridges span the Canada–US border in the middle of the Thousand Islands region.

Construction began on Boldt Castle in 1900 at the bidding of millionaire hotel magnate George C. Boldt as a tribute to his beloved wife Louise. Boldt Castle was designed as their summer dream home. A castle rivaling those of Europe, built on the St. Lawrence River, in the heart of the 1000 Islands. However it was not to be, Mrs. Boldt passed away suddenly just months before the completion of the castle. Mr. Boldt was inconsolable and immediately stopped all construction on Heart Island, leaving the property vacant for over seventy years.

The 1000 Islands Tower is a concrete observation tower on Hill Island, essentially on the U.S.-Canada border, but actually located within Ontario rather than New York State. Built in 1965, the tower provides panoramic views over the Thousand Islands of both nations, from a height of 400 feet (120 m) above the St. Lawrence River.

Zavikon Island is home to a bridge that, at only 32 feet in length, is considered the shortest international bridge in the world. It connects a Canadian island with an American island in the middle of the Saint Lawrence River. The boundary agreement that was drafted between Canada and the United States declares that no island can be split into two territories. Two-thirds of the islands in this bunch, the Thousand Islands, belong to Canada, but the total area of the Canadian islands is roughly equal to the other one-third, which are considered to be American territory.