Answer: The McElroy Octagon House AKA the Colonial Dames Octagon House

The McElroy Octagon House, also known as the Colonial Dames Octagon House, is a historic octagonal house now located at 2645 Gough Street at Union Street in the Cow Hollow section of San Francisco, California.

Octagon houses were a unique house style briefly popular in the 1850s in the United States and Canada. They are characterized by an octagonal (eight-sided) plan, and often feature a flat roof and a veranda all round. Their unusual shape and appearance, quite different from the ornate pitched-roof houses typical of the period, can generally be traced to the influence of one man, amateur architect and lifestyle pundit Orson Squire Fowler. Although there are other octagonal houses worldwide, the term octagon house usually refers specifically to octagonal houses built in North America during this period, and up to the turn of the century.