Eggleston Farkas Architects Sorry for the misunderstanding. What you're looking at is a decommissioned military bunker that has been integrated into the design of the house. The original structure was the fire control station for a gunnery at Fort Ward, protecting Puget Sound from enemy attack (which never occurred). The raised platform was where a rotating scope was located, and the lower floor area was where trajectory calculations were done. Fort Ward was decommissioned, part of it was turned into a state park, and other sections, such as this house, are now in private ownership.
This is because, according to the architects, the house sits upon a "hilltop occupied by a decommissioned military bunker." They added a garage adjacent to the bunker but otherwise just lifted the building on the steel columns, turning the artifact into "the world’s coolest play fort."