On Friday, the old Santa Maria della Misericordia “will open its doors as a functioning mosque, its Baroque walls adorned with Arabic script, its floor covered with a prayer rug angled toward Mecca and its crucifix mosaics hidden behind a towering mihrab, or prayer niche.” The project constitutes all of Iceland’s pavilion, and it has evoked more than a little ambivalence, despite a centuries-long Muslim presence in the city.