The rocky mass, shaped like a reclining woman, as viewed from Koufonisia, was one of the most important worship centers during the Cycladic era. Its importance to Greek religion in  prehistoric and historic times is comparable to that of the sacred island of Delos. Remarkable findings including the 'harpist', the 'Piper,' and the figurine 'Propinon' are currently on display in the Archaeological Museum of Athens. Findings in both Keros and Chalandriani, located in the island of Syros, are testimony to the development of the Cycladic civilization (the Keros-Syros period) that flourished long before the Classical Years. The well known however  'Keros Hoard', much of which was stolen and illegally transferred abroad in the 1950s, consisted of marble and clay figurines, utensils, tools, etc. Today part of the treasure, repatriated, is on display at the Museum of Cycladic Art in Athens. Many are those who believe that in antiquity Keros, not Delos, was the gateway to the Underworld where residents placed the bones of their dead. According to legend,  Keros is the island Asteria, where the twin deities Apollo and Artemis were born. At one point a member of the famed Delian League, the island later became desolate.
Pirates used it as a hideout for some time, followed by treasure hunters of various sorts. Today, the island remains uninhabited, used only by some shepherds, and has been designated as an archaeological site. Access is possible only by private boat, or by a vessel chartered in the neighboring Koufonisia. Apart from the archaeological interest, Keros is surrounded by uniquely beautiful waters, ideal for swimming.