Nate exits the under-chambers of the fortress and finds himself in a courtyard, at the base of a large tower. Noticing that the same tower has been drawn on the map he recovered from the U-boat, he scales the tower's outer walls, and on the inside, he uncovers a set of keys that allow him to proceed further into the fortress. Inside, he finds an English helmet and swords, and on the wall, he reads a message that reads, "Fletcher, we have gone to the great tower. I pray that you will meet us there. -Francis Drake." The message is accompanied by a drawing of the tower, and a map leading to it.Pushing further into the fortress, Nate arrives at and climbs the tower, which provides a vista of the Island below. He finds Francis Drake's telescope, and uses it to study a distant harbor, where he sees that the ships that brought Francis Drake to the island lie ruined and almost completely sunk in the water. It dawns on him that Francis Drake may never have made it off the island. He also notices Elena, who is standing near the base of the tower, filming the same sight across the harbor. Two of Eddy Raja's pirates, one armed with an M79 grenade launcher, sneak up to a ledge behind her and prepare to kill her. Nate opens fire on them, and the one with the M79 turns and fires at him instead. The resulting blast destroys a portion of the tower and knocks Nate unconscious.
He is awoken in a jail cell by Elena, who is throwing stones in at him through the barred window. She informs him that it will just take a tug to pull the bars out, and disappears as Eddy Raja enters the jailhouse, carrying Nate's map. Eddy tells Nate that his men are dying, and that they "can't even go outside to take a piss without an armed guard." Nate refuses to cooperate with Raja's threats and demands, saying that he'd rather die than help him. While the two have been talking, Elena has placed a hook on the cell window bars, and attached the hook to a jeep using a cable. She uses the jeep to rip the back wall out of the cell, and as Eddy stares in shock, Nate grabs the map from his hands and escapes through the wall. He climbs into the jeep and the two drive into the jungle, pursued by Raja's men.
As you walk up the stairs, you will appear outside into a courtyard and get attacked by more goons. A few appear ahead, as well as on the higher level of the fort. Climb the stairs as you fight the goons. After taking them out, head over to the winch on the far wall on the left to open the gate below. Climb back down and head through the gate into another yard.
You cannot open the door yet without the keys. There is a black rope hanging above a small, but high platform. Climb onto some stones to get to the rope. Press to use the rope. Nate will swing into a tall stone structure, knocking it down onto some others, breaking them down, so he can climb on them. Climb the structures to reach another high platform, then climb up the wall to the platform above. Climb onto the ledge above, climb around to drop down onto the fragile stone structure below. As the structure begins to tumble, move quickly and jump on the ledge of the tower. Make your way up to the opening at the top to collect the keys. After that, slide down the rope, then climb back down to the yard to open the door.
After passing through the door, walk through the halls and you will come across another courtyard, packed with enemies. Watch out for the turret in the building above. When it's not firing, rush over to the nearby barrier to your right to grab a M79 and take that guy out. Take out the remaining enemies, then head over to the winch on the left side of the yard to open another gate. Head up the stairs, then take out the enemies within the halls. As you pass through the halls, you will approach the turret. More enemies will show up in the courtyard below, so use the turret to deal with them. Once that's done, press forward and head down the stairs. You will eventually reach a dark room. Head up to the table and press to trigger a small in-game cutscene of Nate reading the writing on the wall. A big brute with a Moss-12 shotgun will show up. Take him out, then climb the long stairs.
You will then appear out into another yard where Nate catches view of the tower. Take out the goons that appear, then make your way to the tower. Head to the the left and climb up to some ledges to reach a building ahead. Then climb across some stone structures to reach the wall. Scale the wall to the reach the window. Climb inside the window, and then make your way upstairs. You will then approach the balcony where Nate will use the telescope to spot the boats and Elena. Two goons below will sneak up behind Elena. Act quickly and shoot one of them before Elena gets killed. The other will turn around and shoot his M79 at Nate, triggering a cutscene leading to the next chapter.