When is a foam coffee cup not a foam coffee cup? Maybe when artist Tara Donovan takes thousands of them and, without altering them in any way, places them together in such a formation on the ceiling of Boston’s Institute of Contemporary Art that they suggest a threatening storm cloud. Visiting her show was part of our stay-at-home vacation that autumn, one of the several local events we took time to appreciate as perhaps only out-of-towners normally do. On the chilly morning following our “chef’s whim” tasting dinner at Craigie Street Bistrot (sauteed coxcombs, anyone?), we walked to Harvard Square, Red-Lined it to South Station, then hopped the Silver Line to the ICA, our first time there. The harbor-hugging building itself is pretty spectacular, and it was fun to run into director Jill Medvedow, an old pal from a “previous life,” but Donovan’s show was the magical highlight. The sculptress takes mass numbers of single ordinary objects -- pins, toothpicks, plastic drinking cups, paper plates, plastic straws, tape, mylar strips -- and arranges them into huge self-standing cubes or spheres or hazy walls or floor “landscapes” that make you stop and look and wonder.