Burial at Sea Episode 2 for Bioshock Infinite has a couple of Coded Messages which can be found to unlock the DLC’s only optional side-quest which takes place in Atlas’ secret lair.
Bioshock Infinite: Burial at Sea Episode 2 Coded Messages Locations
The quest unlocks after you collect one of the four Coded Messages. However, it is advised that you find them all. Furthermore, note that all these messages can be found inside the departmental store while repairing the Suchong’s Machine.
Coded Message #1
Location. Head inside the Bathysphere Services Bay and you will see two mounted turrets. Get past them and look for the message sitting on a nearby table.
Coded Message #2
Location. Head inside a restaurant with a sign reading ‘Food’ on top it. Go all the way to the back and the code will be sitting on a small desk.
Coded Message #3
Location. This message is also found inside a restaurant with ‘Medicine’ sign outside. Once you are inside, look for the message on a small desk.
Coded Message #4
Location. After you have talked to Atlas about the Old Man Winter Plasmid Store, head over to the Test Drive and enter Old Man Winter Plasmid Store to find the last message on a table.
How to Unlock the Secret Lair
Once you have collected all Coded Messages, head over to Manta Ray Lounge and go all the way to the back-left side of the area to reach the Executive Suites.
Once inside, interact with the three wine bottles to unlock the lair.
Found anything missing or confusing, let us know in the comments below!