Sam Hill House, Historic house in Capitol Hill, Seattle, US.

Sam Hill House is a Classical Revival mansion of concrete block construction at 11,000 square feet and five stories, not four. Built 1909–1910 by architects Hornblower & Marshall, it has formal terraces, steel beams, hardwood floors, gas-lit exterior lamps and a secret passageway from the master suite.

Railroad magnate Samuel Hill commissioned architects Hornblower and Marshall to build this house in the early 1900s. The residence was designed in anticipation of a visit by Belgian royalty.

Guendolen Plestcheeff, a Seattle society figure and preservation advocate, bought the house in 1937 and lived there until her death in 1994. In 1987 she established the Plestcheeff Institute of Decorative Arts on the premises. The house remains private and is not open to visitors.

The house is privately owned and not open to visitors; it can only be seen from the street within the Harvard-Belmont Landmark District. The grounds, including Seattle's oldest sundial, are not accessible to the public. The surrounding Capitol Hill streets are residential, so view the exterior quietly and on foot.

The house was an early adopter of hollow concrete block construction, a building method based on a 1898 patent. This innovative technique was uncommon for large residential buildings at the time, making the project an experiment with new materials.