Beaches on Koufonisia were truly great. Finikas and Pori are the best. However, there is nothing more than that: gorgeous beaches. No sites to see, no nightlife and quite crowded in late August. I went to Koufonisia by boat from Naxos for four days and I believe they were enough. The only village is on Pano Koufonisi. Kato Koufonisi is totally uninhabited. Book early because hotels on the island are few.