Sea of Doors
When you regain control, you will be in a familiar area that fans of the first 2 Bioshock games will recognise immediately. Follow Elizabeth through the nearby door and onwards until she gets into the bathysphere. Inside, pull the lever.
When it surfaces, climb the steps and enter the lighthouse. Follow Elizabeth down the stairs to the left and across the bridge that forms for you, you can take the bridge to either the left or right (I don’t think it makes a difference). When you reach the next lighthouse enter the door.
After a brief conversation, again follow Elizabeth across the bridge as it forms and when you reach the next lighthouse go through the door.
Now walk up to the man in front and hit the button prompt when required. After the scene climb the hill behind the pool and enter the door there.
Walk into the door on the right. Interact with the object in here and give it to the man in the doorway.
Open the door again. We are back on the boat from the start of the game. When you reach the dock, climb the ladder and make for the lighthouse. Enter the door here.
Approach the people in the distance and hit the button when prompted.
When you regain control, head up and interact with the door on the left. Wait until Elizabeth stops talking and then enter the tear that she opens.
We are back on the boat from the start of the game. When you reach the dock, climb the ladder and make for the lighthouse. Enter the door here for a scene to end the game.
Congratulations, you have just finished Bioshock Infinite!
Note: For completing the game you will also unlock 1999 mode.