One of the reasons Suyama Space is my favorite gallery for large one-off installations are the skylights facing east and west above the creaky wooden floors of what used to be a garage. Yet for his new CASCADE, New York artistIan McMahon has mostly blocked those clerestories with drapery that’s actually solid plaster. There are portals held open like stage curtains on the east-west axis; once you’re inside the rectangular enclosure, it’s much darker. At the opening reception last month, people seemed eager—on a late spring evening—to herd along the gallery walls, where the sun still crept through. There, too, as if backstage, is the wooden scaffolding McMahon used to install the thing. The dimming effect inside is familiar from theater: When the lights go down, it’s time to hush, turn off cell phones, and unwrap cough drops. The scene was more festive and noisy at CASCADE’s unveiling, but there was the same sense of a threshold, of a boundary between realms. In this case, there will be no swelling orchestra or actors striding onstage. McMahon’s curtains announce nothing but themselves. Divvying up the space is the spectacle; the set, if you will, constitutes the entire show. Every night is opening night in a production that will run longer than any of Seattle’s summer theatricals. Hold your applause; there’s no one there to hear it but you. Suyama Space, 2324 Second Ave., 256-0809, suyamaspace.org. Free. 9 a.m.–5 p.m. Mon.–Fri. Ends Aug. 15.