A challenging site in the Hoyt Arboretum is the setting for this architect's house near the Japanese Gardens. With a very steep and narrow site this 2100-square-foot urban treehouse bridges its living areas and garage to the street. The upper level plan, with its open living areas and den, incorporates floor-to-ceiling southward windows that provide generous natural light and unobstructed forest views. The lower level plan is centered around a central stair with large skylights for further illumination. The master bedroom and master bath open onto a large linear deck, while a separate large bedroom opposite can double as an office/apartment with its own entry and deck.