This mission will become available after you collect all twenty four Peg Leg Trinkets and bring them to the man in the port.
After reaching the abandoned building, run forward and climb onto the wall on the left.
Slowly move in the same direction and jump onto the chandelier to reach the upper floor.
Go through the destroyed door and keep heading onwards until you reach the museum marked with a green point.
There you will find traces which will lead you to the map. The first one is the broken display window on the left, the second the blood stain on the floor and the third the broken vase by the entrance. Eagle Vision will help you in finding them. They will be marked with a magnifying glass icon.
Optional objective: Reach the assailant's location within the time limit - 1:00.
Examine the last trace, turn around and quickly climb onto the balcony on the other side of the museum.
For that, you will have to climb onto the bear on the right and afterwards jump along the wooden beams to the end of the room.
Grab onto the elephant fangs and further onto the big metal object on the right.
As you climb it to the very top, you will be able to jump left and onto the marked balcony.
After reaching your destination, examine two traces: the musket on the left (behind the wolves display) and the mask to the right of the wolves.
After the short cinematic, push the marked shelf and head onwards.
On the left you will find organs which you can climb up. Your destination will be marked on the map with a green point.
After reaching the empty bedroom, slowly move through the hole to the right of the desk. That way you will return to the main room.
There you have to find three traces: a musket leaned against a pillar, a bloodstained clock and another blood stain.
Optional objective: Solve the riddle within the time limit - 1:00.
Optional objective: Completed all the constraints in one playthrough.
When you're done, use the old clock and set the time to 5:50 with the analog sticks. This time is displayed by other clocks inside the cabinet on the right.
That way you will open a secret passage leading to a map fragment.