Once you have returned from any one of your Desmond road trips, you will have obtained a power source that can be used to power up the ancient temple. There are three different control panels that we will need to insert the power sources into. Placing a power source into a socket will open a route to the subsequent power source panel. Once all three of the sources have been inserted, a bridge will form beyond the blue holographic wall.
Power Source 1
Power Source 2
Power Source 3
Congratulations, you have completed Assassin’s Creed III!