The Apollon Theater is one of the most surprising buildings in the Cyclades — a proper opera house in miniature, with three tiers of gilded boxes, a painted ceiling, and the kind of hushed acoustics that make even a modest performance feel ceremonial. It was built in 1864 when Ermoupoli was at the height of its commercial power, funded by the wealthy Syran merchants who wanted their city to have everything a European capital had.
Today the theater still hosts performances, particularly during the Cycladic summer festival season. Check the program before you visit — catching a concert or a recital here is one of those experiences that stays with you. Even without a show, the interior is sometimes open for visits during the day, and seeing it is worth the walk up from the main square.