The Long Beach Marina is a marina near Los Angeles, California.
Ben organized a meeting at the marina between himself, Jack, Kate and Sayid. Sun followed them there, with Aaron asleep in the back seat, with the intention of killing Ben as revenge for Jin's death. ("The Little Prince") When she confronted Ben at gunpoint, Sun learned Jin was, in fact, not dead, and she agreed to go to the Lamp Post with Ben and Jack to find out more about her husband. ("This Place Is Death")
Later on, Ben went to the marina before boarding Ajira Flight 316 so that he could finally exact his revenge on Charles Widmore by killing his daughter Penelope. He shot Desmond, but was distracted by Desmond and Penelope's child long enough for Desmond to recover and attack Ben. ("Dead Is Dead") Ben phoned Jack from the Marina before they all boarded Ajira Airways Flight 316, requesting that Jack pick up Locke's body from Simon's Butcher Shop. ("316")
In the afterlife, Desmond and Charlie crashed into the water near the Marina. Charlie wrecked the car in an attempt to cause Desmond to have a vision of "spectacular, consciousness-altering love." ("Happily Ever After")