This page of the trophy guide for Far Cry 6 explains how to unlock the Didn't See That Coming! trophy. The premise is to use the security control room to disable all cameras and alarms. Below we have described a sample location where you can get the trophy.
Sample location for the trophy - Valle Prehistorico
You can get this trophy in many different locations. This can be any enemy base that has a Security Control Center.
The example image above shows an FND base with the security control center called Valle Prehistorico - that's the El Este region on the world map.
If you have already captured the location from our example, then visit other FND bases in other regions of the map. Try to search each base to locate a potentially locked passage to the security control room.
Using the security control center
Once you get there, do not destroy the cameras or turn off the alarms. Perform a recon and start sneaking around, either killing the encountered soldiers from hiding, or avoiding them.
Your target is an enemy officer - you must kill him and take the access card from him.
If you're detected, you can pause the game and restart the FND base mission.
You have to get to the caves located below the base by e.g. using the climbing kit at a large hole and lowering yourself on a rope.
In the caves, you will find a door leading to the security room and you need to use the recently acquired access card on it.
Find the security control center box. Interacting with it will disable all local security systems and reward you with a trophy.