George Boldt was a wealthy entrepreneur, who made his fortune in the hotel business. He and his much younger wife Louise had become enchanted with the thousand islands and by 1900 had spent a number of summers in the region on his yachts and mansions. He purchased Heart Island and several other islands in the area and in 1900 began construction on a landmark castle in the German style. It was to be six stories with 120 rooms, a powerhouse, huge tunnels, swimming pool, boat house on a nearby island, and the list goes on. This was to be a monument to his love for his wife.
Three hundred workers were used in the construction. The tower building called the Alster Tower, which resembles a defense/watch tower on the Rhine River, was their home while they were on the site. The construction continued for four years until disaster struck. Louise died suddenly at the age of 41 in 1904. George Boldt sent a telegram to the work site ordering work be stopped on the project. He never returned to Heart Island and left the unfinished castle as a mark of his love for his wife.
The castle was left abandoned for 72 years to the weather and casual use by others. It suffered a great deal of damage and decay during these years of neglect and vandalism.
Finally, the properties were turned over to the Thousands Islands Bridge Authority, on the condition that all monies obtained from the use of the property was to be used for restoration.
After over 100 years of history, the castle and grounds have never actually been lived in except for the brief periods that Boldt and his wife stayed in the Tower during those four years.