Poseidonia Club or Poseidonia Center was founded in 1922 in the center of the village and it has served as a country club for the rich holidaymakers in Syros. E. Tsiropinas and G. Psiakis had originally bought this land by A. Manghos. Its construction had begun thanks to the financial contribution of 28 of the regular visitors of Posidonia, who offered 125.000 drachmas. The Posidonia Club was a place for them to get together, to play cards, to dine with music and dancing. The club often hosted theatrical plays and Greek shadow play shows (or Karaghiozis).
The tennis court in its premises is one of the first to be built in Greece.