Milos, Kimolos and uninhabited Polyaigos are a set of volcanic islands in the Western Cyclades (photos above from my visit to Milos in 2017). These islands are characterized by their otherworldly seascapes and amazingly crystal seas. Milos has a long history that begins before the Bronze Age–and was a major source of obsidian in ancient times. It is where the famous Venus de Milo (now in the Louve) was found and in 416 BC, Milos was infamously punished (massacred) by Athens for not paying tribute. It is an island rich in minerals (center photo from the old sulfur mines). As the winds can get quite strong on these islands, the best time to visit is in June to early July. Sometimes the Meltemi winds (that can ruin beach holidays on the islands) have finished by late August and early September. Here is more on Milos and here. And here about Kimolos and Polyaigos