Kalymnos has most of all nice and easily accessible beaches. In general, it is nice and tranquil. However, if you want to really relax, choose an accomodation in the villages, because Pothia in summer is like staying in a big city. I enjoyed hiking along the countryside and lying on the beaches, under the hot sun. In fact, I got sunburn once but I didn't mind. My favorite villages were Emporios and Myrties, really picturesque. The only bad point was the long trip to go to Kalymnos from Piraeus but at least the island was well-connected.