Infinity Island is an island headquarters of the League of Shadows, located somewhere in the Caribbean Sea. The League has a vast fortress complex on the island, with modern security and numerous guards. It also has a Lazarus Pit.
Matt Hagen convinced Talia al Ghul to give him access to the Lazarus Pit. However, because he had deceived her, she locked him inside.
Infinity Island July 8, 22:18 ECT
Sensei briefed his assassins on their next target, Selena Gonzalez.
Serling Roquette was held prisoner on Infinity Island after her kidnapping, and forced to create the Fog. Red Arrow infiltrated the island and rescued Roquette.
After being killed on a mission at
Cape Canaveral, Ra's al Ghul's body was revived in the Lazarus Pit. Moments after he left, Hagen rose from the pit, and attacked them until he was put into an inert state by Ra's. 
Red Arrow, under cover in the League, rested on the island with his partner Cheshire. He began to see some good in her.
After his cover was blown, Red Arrow was able to escape the island with Cheshire. They fled to
Weisman, Greg (w). Vecchio, Luciano (a). Atkinson, Zac (col). Sienty, Dezi (let). Chadwick, Jim (ed). " The Pendulum" Young Justice 12 (January 18, 2012), New York, NY: DC Comics
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Weisman, Jon (writer) & Oliva, Jay (director) (February 11, 2011). " Infiltrator". . Young Justice Season 1. Episode 6. Cartoon Network.
Weisman, Greg, Kevin Hopps (w). Jones, Christopher (p). Davis, Dan (i). Atkinson, Zac (col). Sienty, Dezi (let). Chadwick, Jim (ed). " The Pit..." Young Justice 11 (December 21, 2011), New York, NY: DC Comics ↑ 5.0 5.1
Scott, Sharon, Brandon Vietti, Greg Weisman (writers), (November 19, 2013): Young Justice: Legacy Red Arrow diary #6. Santa Ana, CA: Little Orbit