Sustainable Products, Projects and Green Design Grotto Washroom by Ida&Billy Architects A bright grotto–a contemporary abstraction of nature–is the design concept for this underground washroom. Sustainability, spatial sculpting, human comfort drive the design. The grotto retains the original layout, uncovers two round, tilted square columns to form a unique white mass; seamless curve surfaces diffuse light and omit dirty edges. Plants, irrigated by filtered greywater, purify the air, add life and colors. The original sandstones are crushed as gold aggregates of the new terrazzo floor. Integrated tap-hand dryer, waterless urinal and toilet largely reduce water-use and waste.