BATHYSPHERE STATION
Follow the all-knowing arrow's lead, going east into another bathysphere port. As you approach the pod, the bathysphere takes off without you as you receive a message from Sander Cohen.
Double-back to the previous room, but be careful. There are newly-set electrified wire traps all over, and a pack of spider splicers roaming the room (and the ceiling). When you've cleared the room, go south to the Lower Atrium.
LOWER ATRIUM
The large area's pretty empty for now, though if you go exploring you'll want to watch out for a security camera mounted over the vending machine to the south (it's easy to hack).
The all-knowing arrow wants to lead you up the stairs in the center of the Lower Atrium, but there's a lot of space to the south that you can explore right now. Since we're fans of exploration, we suggest going south where you'll run into a couple of splicers. There are bathrooms to the left (east), inside one of which is a turret (be careful).
There are some more side rooms a bit further south, including the Sophia Salon. Be aware that exploring some areas will trigger the spawning of spider splicers on your way to the Cocktail Lounge.
UPPER ATRIUM
The all-knowing arrow urges you westward once upstairs, but there's a room to the south you might want to explore. Watch out for a mounted turret on the upper walkway of the room that guards three safes. You can hack the safes to collect some worthwhile goodies before following the wisdom of the arrow.
You'll go west into a parlor with a security camera on the western wall. The camera is easy to spot and easier to dodge so you can hack it from underneath. To the north is a stairway that leads to an upper alcove that's half blocked-off. For now, just go back downstairs.
On the southern wall is an elevator. Call the elevator to you via the button on the wall and be ready for a few splicers that invade the room from the stairs to the north. Take 'em out, then ride the elevator into the Fleet Hall Theater.
FLEET HALL THEATER
Don't be alarmed by the pianist in the spotlight. Approach him and he'll play his tune under the demand of Sander Cohen. Eventually, somethinghappens, and Sander Cohen asks you to photograph the pianist with your camera. Take one photo of the pianist (but only after Cohen's asked you to).
Before leaving the theater, go to the southern end of the upper level. There are doorways that lead to small balconies overlooking the stage, and on the balcony to the far southwest is a tonic. Unfortunately, the doorway to this balcony doesn't open for you. You'll have to step onto the balcony just east of it, then jump from one balcony to the other to grab theAlarm Expert tonic.
Expect a few Houdini splicers to congratulate you on your find (by attacking you, of course). Make your way back downstairs and out the doorway through the north, but beware a pair of security turrets mounted just north of the theater's exit. If you can get by them, there's a safe in the back corner that you can hack open.
UPPER ATRIUM
The all-knowing arrow leads you back to the Upper Atrium and then downstairs. At the base of the stairs is a massive sculpture. To complete the current task, walk up to the sculpture and activate one of the empty frames to place the photograph you've just taken. Cohen should then give you a new set of tasks. Before embarking on the new quest, grab the cross bow in the hands of one of the sculpture's characters.
Go back upstairs and continue east from there. The doorway to PoseidonPlaza will open up for you, letting you continue down a frozen hall