Connected to the main house by a narrow bridge, a three-story cedar tower with a sauna at its base recalls a tree house. The screened-in second level includes a table and chairs for enjoying an outdoor meal, while a swing on the tower’s top level provides a perch to take in the surrounding birch trees.

Translucent fiberglass panel walls form a permeable, fiber-reinforced plastic membrane between indoors and out.

For an escape from bustling San Francisco, architect Craig Steely and his wife Cathy have created a modernist getaway on a lava field next to a black sand beach on Hawaii’s Big Island. Fitted with floor-to-ceiling windows that look out over the ocean, the steel-framed home is one of several homes that Steely built on the recently active lava field.