In one word: Close (to Fira), 
GPS: Just two kilometers from Fira. It has good marking and will need to follow the road that turns at the entrance of Kontochori.
Picture: A beautiful little bay with black sand and pebbles with volcanic background.
Beach Life: A few chairs and a restaurant. You do not need anything else for a beautiful beach day in Santorini.
People: Mainly couples who love privacy.
Food/Drink: From the tavern you can have water, coffee and soft drinks and a local cuisine and fresh fish meal all day long.
After beach: Feed the swans in the nearby small harbor.