The closest beach to Kalamitsi (Sithonia) is Kalamitsi, just 150 m away. Within 15 km there are 30 beaches; below are the 12 closest to Kalamitsi, ordered by distance. Photos, map, reviews.
150 m from Kalamitsi

530 m from Kalamitsi

750 m from Kalamitsi

4.3 km from Kalamitsi

4.9 km from Kalamitsi

4.9 km from Kalamitsi

5.0 km from Kalamitsi

5.1 km from Kalamitsi

5.2 km from Kalamitsi

5.5 km from Kalamitsi

6.3 km from Kalamitsi

6.5 km from Kalamitsi

Kalamitsi, just 150 m from Kalamitsi. The rest are listed below, ordered by distance.
Within 15 km of Kalamitsi there are 30 beaches, with 69 across Sithonia in total.
Based on user reviews: Klimataria Beach (★4.7), Kalamičti Nudist Beach (★3.8), Kalamitsi (★3.5).
The beaches are spread out around Kalamitsi. A car makes exploring much easier — local buses and taxis are limited outside peak season.
Kalamitsi is on the Sithonia side of Halkidiki, in northern Greece. The nearest airport is Thessaloniki (SKG); from there a car is the most convenient way to reach the Sithonia villages.