This fun installation, GiRA, in Porto, Portugal by the Micro Atelier de Arquitectura e Arte (MAARQA) celebrates the city's traditional midsummer festival of St. Jaoa, in which citizens greet one another with flowers and soft, plastic hammers. The sphere of hammers can be manipulated by passersby, inviting them to become an active part of the celebration and the festival's history. Perhaps most importantly, MAARQA feels this public object infuses the city with a feeling of play and whimsy. Visit the firm's website to see more photos of GiRA and and read about their other fascinating installations.