Dr. Fisk Holbrook Day, Wauwatosa's most prominent citizen, was a highly regarded physician and a member of many societies that reflected his varied interests. Day was most devoted to amateur geology and paleontology as seen in his rock and fossil collections, many taken from nearby quarries and outcrops, where he made detailed scientific observations.

Day commissioned noted Milwaukee society architect James Douglas to design Sunnyhill Home in 1874. The High Victorian mansion was set far back from the street and atop an imposing hill in order to give an impressive appearance. It was constructed with local Cream City brick, for which Milwaukee is famous. A low-pitched pyramid caps the multi-colored Mansard roof. The front is composed of slightly recessed bays and prominent bay windows. Many elaborate details such as ornamental scrollwork and engaged columns adorn the building.

Day incorporated a "Cabinet Room" into the plan of Sunnyhill. Towering display cases housed collected artifacts, historical documents, and works of art, minerals and other natural history specimens from around the world. Collecting specimens for one's own "cabinet" was a popular Victorian pastime, but few pursued it with Day's vigor. He built a nationally prominent fossil collection that formed the backbone of public collections, such as UW-Milwaukee's Greene Museum.

The house is a private residence; please respect the privacy rights of its owners.

This property was designated a National Historic Landmark in 1997. The Landmark listing name is the Day, Dr. Fish Holbrook, House. NRIS #97001268.