Tasked to design new prototypes of spaces and activities on Market Street, to be up for 3 days, for the Market Street Prototyping Festival, we created a space of respite on the busy sidewalk. sonoGROTTO is an experiment in using affordable, ubiquitous, and recyclable materials to create new human-scaled spaces on the cavernous and over-scaled corridor. It is composed of 235 cardboard tubes fastened together. The tubes were packed, trimmed to fit within a 10-foot cube, and was carved creating seats, windows, and an oculus to view the sky above. Digital design and modeling enabled the production of full-scale surfaces that were used as templates to fabricate each individual tube. As the day passes, revolving arrays of dappled-light and shifting shadows dance in and around the vicinity of the grotto. sonoGROTTO proved itself to be successful in engaging the public, fostering interaction, and provided human-scaled space. It is an economical and adaptable system that can be deployed for short-term events, as well as be a template for more permanent urban installations.