Train Robbery
The Train is always visible on the map, though it may require some searching to locate its current location. Once you’ve found the icon on the map, place a marker on it to highlight its location. Each robbery rewards £3750, 563 XP, and 250 assorted materials, in addition to whatever loot you find aboard the train.
Boarding the Train
Once you’ve deciphered the train’s direction on the rails, head for the nearest train station in the direction it is heading. The train stops at the station, making boarding it as simple as walking up and hopping on.
Board the train from the front and immediately de-couple the engine from the rest of the train cars. You do this the same way as in Sequence 3, by pressing 
/ 
then 
/ 
repeatedly. With the train cars uncoupled from the engine, you don’t have to worry about catching back up to the train if you fall off.
Finding the Treasure
Use your Eagle Vision to scan the carts. The treasure is in a small briefcase and is highlighted in yellow. If you’ve stopped the train, you can jump off the train and walk to the car, bypassing any enemies that may be between you and the treasure.
Completing the Robbery
Once you’ve collected the prize, leave the train in any direction. When you get far enough away from the train the activity completes.