Having called irony “the most human way to express yourself,” the 37-year-old musician and prankish durational performance artist, who represented Iceland at the Venice Biennale in 2009 with a 6-month on-site painting marathon, now presents a nostalgic, visually sumptuous 9-channel video installation on the theme of regret. Viewers wander among large screens showing hip, semi-catatonic young musicians, each isolated in a different part of a decaying 200-year-old mansion in upstate New York, playing instruments and repeatedly singing a lost-love lament. The single most memorable segment of The Visitors, titled after the Swedish group ABBA’s 1981 breakup album, features Kjartansson himself mournfully strumming a guitar and crooning in a soapy bathtub.