Hi Jacqueline,
There is a beach called Golden Beach which is a few miles past Pefkohori, It is a nice sandy beach with pine trees surrounding the area. This beach in the past was known for nude sunbathing and was popular with the German tourists at the time. If you take the Paliouri bus ask to stop at the three brothers taverna which is on the main road and you can then walk down to the beach from there.
In general Halkidiki really has some beautiful beaches and if you walk along the old coast road you should be able to also find a spot.
