Gioura or Yioura is one of the islands in the Marine Park of the Sporades and it is situated north of Alonissos, just above the island of Kyra Panagia or Pelagos. The island has rocky shores and a mountainous island which is covered with low shrubs. Gioura is famous for its cave of the Cyclops, a large cave with stalagmites and stalactites, which reputedly was the original dwelling of the Cyclops. The island of Gioura has no harbour. The underwater caves and the seas around the island are home to the endangered Monk Seal and inland you can find rare species of birds and birds of prey. There is also a unique species of wild goats that live on the island. There are permanently one or two guards on the island in order to protect the wildlife on and around the island.

Excavations that took place in several parts of the cave of the Cyclops have shown that the island was already inhabited in the Middle Neolithic period, since painted potsherds, bone tools and fish hooks from this period were found. Pottery from the Bronze Age have also been found. The Roman remains on top of that consist mainly of oillamps that are decorated in relief or inscribed, implying that the cave served as a sanctuary around the 2nd and 3d century A.D. Also remains from the Hellenistic period have been found deep inside the cave.