You can explore the cave of Agios Ioannis (or Ai Yannis) with its stalactites, stalagmites and columns near Vourkaria bay to a depth of 120 metres. The cave – in reality two caves opposite each other – also functions as a church. It features spilaiogala (translated as cave milk, which is rare stalagmite material in liquid form). This is one of the largest caves of the Cyclades and certainly one of the most amazing ones. The feast of Saint John takes place here with people coming from surrounding islands as well.