Once crammed into a tiny building in Back Bay, the ICA is now the cultural cornerstone of the Seaport District. (Across the water in East Boston, the ICA Watershed is a seasonal satellite gallery, open Memorial Day through Labor Day.) The dramatic, glass-walled building houses galleries, a theatre and a café. The museum prides itself on being a platform for challenging works, while changing shows explore broader themes that unite different artists' work, or focus on individual luminaries. After you've contemplated the art, retreat to the scenic outdoor harbor deck, site of numerous performances and events. Note: Admission is free on Thursdays from 5pm-9pm.