Fly Like an Eagle – Jump with the Parachute from the Top of the Castle San Angelo.
First you need to have a parachute. You can get this by completing all missions for Leonardo Da Vinci and destroy his war machines. After doing this, Leo will reward you with a parachute and you can later purchase it at the tailor.
Once you have a parachute, just replay DNA Sequence 8, Memory 2: An Apple a Day (Beat Cesare to the Apple of Eden). You will find yourself hanging on the Castello.
Go to the top of building and you will see a pole.
Climb on top of the pole then jump using the parachute then you will be flying like an Eagle.
You will get 10G for the XBOX 360 and a Bronze Trophy for the PS3.
For a full detailed walkthrough, you can watch the video here on how to do this.