Spanish architects Jose Selgas and Lucia Cano of Selgascano have designed an office for their own practice, located in the woods near Madrid in Spain. (Pics)

A 20mm thick, curved window made of transparent acrylic forms the north-facing wall of the tunnel-like space.

The opaque, south-facing aspect is constructed from a 110mm thick, insulated, fiber-glass and polyester sandwich, offering shade from direct sunlight.

A hinged opening attached to a weighted pulley mechanism at one end of the building allows varying degrees of natural ventilation.

Via Dezeen