Lissos beach is not sandy; the coast has large pebbles and is exposed to southerly winds. But it is quite isolated, so you should be equipped with what you need before you get there for diving.
The trees surrounding Lissos beach will offer you shade and bring relief from the hot summer libeccio (south-westerly wind).
Within walking distance from the beach is the chapel of Agios Kyrikos. If you are there, on the 15th of July, it is worth to take part in the festival, which is in honor of the saint.
To reach Lissos beach, you should take the boat from Sougia. The journey takes 20 minutes. If you can tolerate walking, you can follow the path that goes from Sougia to the beach. Remember that the journey takes about two hours.