Pserimos Island, Greece.
The only regular service to Pserimos is from nearby Kalymnos, from which the Pegasus leaves in the morning and returns in the afternoon every day through the summer, and more intermittently through the winter.
(From Kos there are only round trip tour boats which are more expensive and always include other stops, as well as food and entertainment, in the price; in order to stay on Pserimos for any time, if you are coming from Kos, it is necessary to negotiate a price with separate boats – one to drop, the other to pick up).
Pserimos Travel Guide
Pserimos Travel Guide – Best of Pserimos Island: History, beaches, places to visit & more.