Discovering the AAF officer’s letter and East Wind intel in Showcase Cultural Property is easier than it might seem, though there are some things you should be aware of.
Where to find the letter (and what to avoid)
Be aware that Showcase Cultural Property is a premium content of the DLC. In other words, you have to actually own Art of War DLC to access the mission, otherwise it will be locked.
Once you land in the beginning of the Cultural Propert mission and deal with the sniper, simply head east to the southern edge of Sofia area. There you’ll hear a single gunshot. You should also see white smoke and one Strider vehicle parked near a chapel. Be aware, though, there is one very much alive enemy hidden in the smoke, who doesn’t hesitate when it comes to some shooting.
As you might already guess, your target is in the chapel, but don’t rush straight in. The area is heavily mined. This is NOT Oreokastro, you are NOT equiped to safely disarm the mines, so tread very carefully or just approach the chapel from a side. Strider marks the safest way.
Once inside, find a letter on the ground and read it. The achievement should pop. As for the contents of the letter, that’s up to you to discover.
Please note: Not all mines are marked in this screenshot.