The closest beach to Sani (Kassandra) is Sani, just 390 m away. Within 15 km there are 13 beaches; below are the 12 closest to Sani, ordered by distance. Photos, map, reviews.
390 m from Sani

1.2 km from Sani

5.9 km from Sani

7.5 km from Sani

8.9 km from Sani

9.0 km from Sani

11.2 km from Sani

11.3 km from Sani

11.6 km from Sani

11.6 km from Sani

11.9 km from Sani

Sani, just 390 m from Sani. The rest are listed below, ordered by distance.
Within 15 km of Sani there are 13 beaches, with 25 across Kassandra in total.
Based on user reviews: Sani (★5.0), Nea Potidea (★4.1), Afitos Beach (★4.0).
The beaches are spread out around Sani. A car makes exploring much easier — local buses and taxis are limited outside peak season.
Sani is on the Kassandra side of Halkidiki, in northern Greece. The nearest airport is Thessaloniki (SKG); from there a car is the most convenient way to reach the Kassandra villages.