Youra is an island in the Northern Sporades chain, off the coast of Greece. Uninhabited, it is mostly desert and mountain, and has no natural harbor. The so-called 'Cave of Cyclopes' at the southeastern end of the island contains archaeological evidence of both prehistoric occupation of the island and occasional stopovers by ships during the classic period.
It was used by Mistra as a temporary base of operations after they had to flee North America and regroup in the face of the ongoing government investigation of their activities and the loss of their field leader, Morgan, in combat with the X-Men in Canada. The X-Men and the freed operatives led by Colin MacInnis, in cooperation with the US government, would later invade Youra, leading to a costly battle that took Mistra down for good but left many dead on both sides.
Afterwards, the Greek government reclaimed their sovereignty over the island.