Lian Yu is the name of the island in the North China Sea where Oliver Queen was stranded for five years after the Queen’s Gambit sank. It is also the place where Oliver buried his father. The name of the island means purgatory in Mandarin.
The island was used as a prison until Edward Fyers ordered the execution of all the inmates. Yao Fei and Slade Wilson are the only known survivors of the massacre.
While on the island, Oliver was captured by Fryers men and tortured by Billy Wintergreen. He was rescued by Yao who became his mentor and trained him to become a fighter and marksman.
After The Undertaking, Oliver returned to the island believing he had failed Starling City. He felt that his mission as the vigilante and The List was a fool’s errand. Felicity and Diggle go to the island and convince Oliver to come home.