The Cyclops Cave lies in the southern part of the rocky and hostile island of Yioura. Yioura belongs to the island group of the north Sporades, about 20 miles from Alonnisos.

The Cyclops Cave is situated 150 metres above the sea level and its size (60X50) and height (15 m) makes it the biggest in the north Sporades. Excavations conducted in its interior (1992-95) have provided evidence of continuous human activity from the Mesolithic Period (10,000-6,800 BC) throughout the Preceramic Neolithic (6800-6500 BC), up to the Late Neolithic Period II (LΝ II) and the beginning of the Final Neolithic (4600/4500-3300/3200 BC). The cave was used also during Historic times (Classic-Roman Period).

The sections excavated at the mouth of the cave unearthed anthropogenic layers rich in stone and bone artefacts, ceramics, animal and fish bones and shells.

Evidence from the layers of the Mesolithic period at a depth of 1,8 m suggests that the cave was used intensively during this period and this find is particularly important for the Aegean Prehistory. Stones and animal bones confirm that hunting was practised, whereas the plant remains and many shells and snails provide evidence of continuous gathering. Hundreds of fish bones mainly of tuna, and a number of fishooks (approximately 45) in different sizes (6 mm-7 mm) indicate that intensive fishing with advanced tool equipment took place.

Since this marine location is still a passage for tuna mainly in autumn, it is possible that the Cyclops Cave was inhabited periodically by specialized fishermen from neighboring islands which were intensively populated during the 9th-7th millenium BC (Alonnisos). At the beginning of the Holocene travelling from one island to another along sea passages was probably conducted by primitive means (rafts). Navigation is attested in the Aegean in the middle of the 9th millenium by the artefacts of Melian obsidian found at Franchthi Cave in Hermionid.

At the Cyclops Cave, in layers of the 9th millenium, part of a woman's skull was found whose age has not yet been definitely determined. Anthropological material date to the Mesolithic period are also known from burials which were found at caves in Attica, at Franchthi in Hermionid, at Theopetra in Kalambaka and at Maroulas on Kythnos.

Among the finds of the Mesolithic, shell-ornaments and limpet shells, which were turned into spoons after special retouch, were discovered.