If you look at a map or satellite image of Kassandra, it resembles a sort of spindly-looking stocking-wearing foot pointing in a southeasterly direction. To the west, at the end of the heel, is the small resort village of Possidi. At the very tip of the heel is the sandy point of land known as Cape Possidi. It has a lighthouse set back from the water, at about the point where vegetation starts growing, as the sands of the cape are forever shifting. The sand narrows to a bar as it extends into the water, and then, at the very end, curls back on itself like a comma. Setting your umbrella up near the end of the cape is an interesting choice, as you get two beaches for the price of one, with maybe 10 meters of sand separating the two.
It's a fantastic, little-known place to spend a day at the beach, as long as you have your own shade, food, and drink with you. Heading up the west coast, or the "back" of the heel, are a number of hotels, maisonettes, and nice beaches on up to Skala Fourkas, 5km away. There are a couple of campgrounds, one run by EOT, the Greek Tourism Organization, and another run by the Aristotle University of Thessaloniki, offering organized group camping for university students, young kids, or young people involved in the arts, depending on what time of the summer it is.
Going east, along the south coast of the cape, or the "bottom" of the heel, its a couple kilometers to the resort village of Possidi. On the way you pass a beach bar with sun beds, umbrellas, and tables in the shade of the pine trees where you can take a break, sip your drink, listen to the cicadas in the trees, and admire the view of the beach and the sea.
Possidi village only has about 35 year-round residents. It was built for, and does a good job of serving, tourism. There are a number of places to stay covering a range of prices.
The south-facing Possidi beach has a very nice promenade made of landscaping pavers and bordered with palm trees. There are a number of beach bars, restaurants, cafes and tavernas to choose from. The atmosphere is perfect for stress relief. You can eat your meal of fresh fish and enjoy the mesmerizing sound of the waves on the beach. There's not a lot of night life at Possidi, which is nice if sleep is your priority at night.
If you want to try a different beach, it's just a few minutes' walk across the peninsula to the northwest-facing beach, which is called Ageopelagitika (where the campgrounds and some other resorts and hotels are). Some visitors report that Ageopelagitika is a nicer beach. It also gives you a clear view of Mt. Olympus across the Gulf of Thermi.
Close to Possidi is the complex of ruins which served as the sanctuary for ancient Mendi, whose ruins are to the east about 4km from Possidi. Excavated structures include the temple of Poseidon, dating from the 5th century, and a building that lays claim to being one of the oldest temples in Greece, dating from the 10th century, BC. There is also an altar dating from the 12th century, BC.