Simply Find 100 Audio Diaries scattered around Rapture for this achievement. So here are the first 100 Audio diaries in the game..

THE BEGINNING


Audio Diary #1 - "Attention Workers!"
Located in the large pool room where you first see a Big 
Sister. On the left side of the room, right next to the 
sparking generator that you use to restore power.

Audio Diary #2 - "Fitness"
Inside the locked steam room. Just use the code written on 
the window to enter.

Audio Diary #3 - "To My Daughter"
After restoring power and entering the unlocked area, 
you'll walk by two restrooms. The audio diary is at the 
back of the women's, or "Dames," room.

Audio Diary #4 - "Return"
Inside the room with the wading pool and fancy arched 
bridge. Find the corner with the "Best and Brightest" 
poster and look on the bench below for the audio diary.

Audio Diary #5 - "They Called It Rapture"
In the room passed the room with the bridge, go through the 
door marked Rapture Metro.The audio diary is on the floor 
with some teddy bears to the left as you enter.

Audio Diary #6 - "Generation"
In the next room, near the Vita-Chamber, check the corner 
of the bar for this audio diary.

Audio Diary #7 - "Escape from Rapture"
During the first underwater walking segment, watch your 
left for a crashed bathysphere pod. It's right before the 
Adonis pillar forces you to jump. Search the corpses inside 
to grab the audio diary.


THE ATLANTIC EXPRESS 


Audio Diary #8 - "The Great Chain Rattles"
You'll enter a large station and watch as a train car falls 
to the ground. To the left of that wreckage is a door 
leading to a Train Workshop. The audio diary is on a desk 
inside.

Audio Diary #9 - "Mr. Tape Recorder"
Once you've obtained the Telekinesis plasmid, return to the 
area where you emerged from the water. Next to those steps 
is a huge fan, with the audio diary hidden behind it. 
You'll need to use your newfound power to pull the diary 
towards you.

Audio Diary #10 - "Just a Fad"
On an upper balcony lined with gas tanks. The game is 
strongly suggesting that you use your newfound Telekinesis 
power to throw those tanks at a gathering of Splicers 
below. Before doing so, grab the audio diary off the 
drafting desk.

Audio Diary #11 - "What Happened to the People?"
This audio diary is in the second large train station - the 
one in which the train car doesn't fall to the ground. To 
the right of that train car, on the platform, near a 
mattress, is the tape.

Audio Diary #12 - "Ryan vs Lamb: Reality"
Go to the very back of the cafeteria, past the kitchen with 
the burning stoves. The audio diary is in a dark storage 
room with windows looking out on water.

Audio Diary #13 - "Know the Beast"
Once you've removed the pipe from the gears using 
Telekinesis, a big door will open. Go through and turn left 
into a hallway, and then left again, and the diary is in 
the corner near the window on an overturned filing cabinet.

Audio Diary #14 - "Improving on Suchong's Work"
Upon exiting the lengthy elevator ride, you'll be in a room 
with Trap Rivets. Up some stairs and to the left is a 
Manager's Office with the audio diary tucked in a filing 
cabinet.

Audio Diary #15 - "The Situation"
Before leaving on the train, search the benches near the ID 
sign for an audio diary.


RYAN AMUSEMENTS 


Audio Diary #16 - "Eleanor's Progress"
As you enter the door up the stairs from the station, it is 
in the corner on the right with the candles.

Audio Diary #17 - "The Old Sheepdog"
In the manager's office, immediately before you remote hack 
through a broken window to open the door.

Audio Diary #18 - "Volunteer"
The middle of the Rapture Museum, beneath a bench that is 
directly between the doors to the Gift Shop and to the Hall 
of Future.

Audio Diary #19 - "Eat Dog"
Can't miss this one. It's in the same gift wagon as the 
Drill Power tonic Eleanor leaves for you.

Audio Diary #20 - "'Child' and Guardian"
Located near the far windows of the El Dorado Lounge, where 
you fight your first Big Daddy.

Audio Diary #21 - "You, Me, and 1959"
Before entering the Journey to the Surface ride, head to 
the Ride Maintenance room on the left for this audio diary.

Audio Diary #22 - "Escape Plan"
On floor next to the second harvest corpse.

Audio Diary #23 - "Lamb the Problem, Sinclair the Solution"
To the east of the second harvest is a pile of crates with 
an Eve Hypo, .50 Caliber Rounds and another audio diary. 
It's right behind some falling water, and also near a large 
neon arrow sign that says "Conformity & Co."

Audio Diary #24 - "Truth is in the Body"
Go through the hole in the wall in the corner just before 
the second Andrew Ryan robot to a series of balconies 
overlooking the track. Diary is on a workbench between two 
of those balconies.

Audio Diary #25 - "Deterioration"
To the right of the animatronic scene with the parents and 
child is a storage room full of giant hands. Climb the one 
in the center as if it were a ramp and you'll find the 
audio diary on an upper balcony. (Thanks to EngieIndeed)

Audio Diary #26 - "Working for Sinclair"
Past the animatronic scene with the parents and child 
watching television is a water-filled room with a Power to 
the People weapon upgrade station. In a room to the right
is an ammunition vending machine and the audio diary.

Audio Diary #27 - "Doctor Lamb"
Under the security camera, go to the left and break down 
the wooden boards with melee to reveal the diary.

Audio Diary #28 - "Efficacy"
On your left just as you pass through the doorway near the 
Lighthouse scene.

Audio Diary #29 - "Dating Tip"
You might have noticed this door before entering Journey to 
the Surface. Once you've opened / unlocked all maintenance 
doors in order to exit Journey to the Surface, this door 
will finally open. Head inside for the audio diary.

Audio Diary #30 - "A Father's Love"
Halfway through the Hall of the Future, next to a Vita-
Chamber.

Audio Diary #31 - "Cutting Corners"
In the far right back corner of the Gift Shop, near a safe.

Audio Diary #32 - "Rapture is Deliverance"
Restroom of the Gift Shop… "Dames" side. You have to 
Electro Shock the locked door to enter.

Audio Diary #33 - "Disappeared"
Trapped in ice near the beginning of the level. Once you 
have the Incinerate plasmid, you can melt the ice and get 
it.

Audio Diary #34 - "Wooden Nickels"
Immediately before boarding the train, look for a newly 
opened door to the left of the previously frozen tunnel
entrance. It was locked when you were here before. Inside
is an audio diary.


PAUPER'S DROP 

Audio Diary #35 - "Ryan vs Lamb: Religious Rights"
Inside Marlene's Flower Emporium.

Audio Diary #36 - "Better Times with Lamb"
On the ceiling of Marlene's Flower Emporium. Access this 
area by climbing the wooden ramp at the back of the 
Fishbowl Diner, then crossing the roof and another wooden 
ramp.

Audio Diary #37 - "Wrong Side of the Tracks"
The front office of the Sinclair Deluxe. You can collect 
this audio diary before clearing the Brute Splicer's 
debris.

Audio Diary #38 - "The End of the Line"
At the makeshift altar to Prentice Mills, in the corner of 
the large Downtown area with the upended train car.

Audio Diary #39 - "Clinic Code at the Fishbowl"
Sitting right outside the door to Fontaine Clinics, below 
the code input.

Audio Diary #40 - "Camera in Hock"
On the desk of R. Flanagan. His office is on the second 
floor of the Hamilton.

Audio Diary #41 - "Arrangements"
After exiting the top floor of the Hamilton, there is a
Little Sister altar full of blue butterflies. The audio
diary is there.

Audio Diary #42 - "Therapy With Grace 1"
From the roof of the Pawn Shop cross the wooden walkway 
to the Luxury Rooms. An audio diary is here.

Audio Diary #43 - "Blood and Lamb"
Go to the "Books" store in the Skid Row section of the 
level. The door will be locked until you access and hack 
through a hole in the back of the neighboring Pharmacy.

Audio Diary #44 - "Mole"
Down the hallway in front of the Pharmacy, there is a
fire with the audio diary nearby.

Audio Diary #45 - "Sunday Services"
Take a right out of the hallway with Diary #44 and another
right into the apartments. Take the second left and the
diary is on a couch.

Audio Diary #46 - "Pauper's Drop"
In a hidden room off the roof of the Pharmacy. Get there by 
taking a wooden walkway from the Skid Row apartments where 
you got the last audio diary.

Audio Diary #47 - "Closing the Limbo Room"
Grace's dressing room in the Limbo Room.

Audio Diary #48 - "A Gift From Lamb"
Bathroom at the back of Room 106, which is on the second
floor of the Sinclair Deluxe. Go here immediately upon
entering the hotel.

Audio Diary #49 - "Profit Coming, Profit Going"
Before moving to the third floor, head right and go up
some stairs. Jump across a gap to grab the audio diary.

Audio Diary #50 - "Where Has Harry Gone?"
Go through door 213, turn left, and to the right of the
turret in this room is the diary.

Audio Diary #51 - "The Butterfly"
Room 212, on the second left in a butterfly room, on the
desk.

Audio Diary #52 - "What A Snap"
Upon reaching the fourth floor, turn right and follow the
hallway to the end.

Audio Diary #53 - "Barbarism"
Tucked under Eleanor's bed in Grace's apartment.

Audio Diary #54 - "Failing Lamb"
Lying on Grace's bed in her apartment.

Audio Diary #55 - "Field Trial #1"
While escaping Pauper's Drop, kill the Brute Splicer you
encounter in the Fishbowl Diner area. Search his corpse
for an audio diary.

SIREN ALLEY (SIA)

Audio Diary #56 - "A Silent God"
Hanging next to the painting of the first BioShock's plane 
crash. On your left as you enter Little Eden Plaza from the 
airlock.

Audio Diary #57 - "Misbehaving"
The counter of the Poisoned Apple bar in Little Eden Plaza. 
To get inside, you must climb up any of the nearby 
staircases and drop through the roof.

Audio Diary #58 - "The Rumbler"
Inside the restroom of the Mermaid Lounge, under a mound of 
frozen ice.

Audio Diary #59 - "Plasmid Shipment"
Upper floor of Mermaid Lounge, on a table in the slot machine
room in the back.

Audio Diary #60 - "Farther to Fall"
Right next to the Mermaid Lounge's weapon upgrade (Power to 
the People) station. To access, go upstairs, shoot a hack 
dart through the bar window to unlock the door and drop 
through the hole in the floor.

Audio Diary #61 - "'Father Simon Wales'"
In an office in the back of the first floor of the Pink
Pearl brothel.

Audio Diary #62 - "Double Standard"
Second floor of the Pink Pearl, in the central room with 
the bed, dead hooker and purple flickering light.

Audio Diary #63 - "Wales ‘an Wales"
Daniel Wales's desk on the highest floor of the Pink Pearl. 
His office is next to the hole in the floor that Daniel 
drops through.

Audio Diary #64 - "The Date is the Code"
Search Daniel Wales's corpse after defeating him.

Audio Diary #65 - "Lamb's Salvation"
Outside the entrance to Plaza Hedone, propped next to the 
door you've spent the first half of this level trying to 
open.

Audio Diary #66 - "The Pair Bond Mechanism"
In Plaza Hedone, the second shopping center of Siren Alley. 
Near the door to the Little Sisters Orphanage, as well as a 
Gatherer's Garden and security camera.

Audio Diary #67 - "Bury Her Memory"
Second level of Plaza Hedone, in a northwestern room with a 
desk and a fridge.

Audio Diary #68 - "The Requirements of Utopia"
In the southwest, ground-level corner of Plaza Hedone are 
two small alleys that meet in a loop. Follow the loop down
all the way to find an audio diary.

Audio Diary #69 - "An Empty Niche"
Find the illegal plasmid lab by hitting the "conspicuous 
switch" at the Green Grocery. At the very back of this 
area, on the bottom floor, you'll find the audio diary
on a table.

Audio Diary #70 - "Lamb's Operation"
Located in the smugglers' hideout, which is above the Green 
Grocery. Most any walkway on the 2nd or 3rd levels of Plaza
Hedone will lead you to this area eventually, but you can go
up the stairs outside the Grocery, take two rights, a left,
two more rights, and the door is on the left.

Audio Diary #71 - "My Name is Eleanor"
Last bunk bed in the group sleeping quarters of the Little 
Sisters Orphanage.

Audio Diary #72 - "Shackled to the Great Chain"
Upon entering Pump Control Substation #5, go left up
the stairs to a locked office. Hack the door through the
grate and grab this audio diary.

Audio Diary #73 - "Guidance of Lamb"
At the candle altar, in Pump Substation #5, before heading
into the "Temple of Lamb." It's underneath the paintings of
the first BioShock protagonist's hands.

Audio Diary #74 - "Therapy with Grace 2"
In the last hallway before Father Wales's church, there's a 
door on your left leading to Sofia Lamb's office and a 
Power to the People weapon upgrade station. The audio diary 
is tucked in a filing cabinet.

Audio Diary #75 - "The Creed of the Faithful"
At the main altar of Father Wales's church, beneath the 
large painting of the butterfly-headed woman. Grab during
the fight or before the place floods afterwards.


DIONYSUS PARK 


Audio Diary #76 - "Patronage"
In the room to the east of the large room with the covered
statues is the audio diary.

Audio Diary #77 - "A Gift From Billy"
Climb up the stairs to exit the first big room with the 
covered statues. Continue down the stairs on the other side
of the landing at the top. This way ends with rubble, but
also an audio diary.

Audio Diary #78 - "Lamb's Time is Over"
When you use Billy's code to unlock the door above, you'll 
find a room with another audio diary.

Audio Diary #79 - "Lamb's Idea of Art"
After climbing a frozen stairwell, in the room past the
ammo vending machine, the audio diary is at the feet of one
of the statues on your left as you enter.

Audio Diary #80 - "Lost and Found"
Center of the carousel.

Audio Diary #81 - "Dionysus Park's Weakness"
In the first room of Basement Storage. Climb up the short 
stairs on either side and you'll find the audio diary 
propped against a flooding door.

Audio Diary #82 - "Lamb Flouts the System"
In the central area between the Theater, Ocean Entrance,
and the hallway to the J. Fischer Gallery and Imago Fine
Arts spaces, the audio diary is near the central statue
of the two women standing back to back with their arms
raised up to the sky.

Audio Diary #83 - "Learning Poker"
Head to the Triton Theater, and take a right to the basement
lounge. At the back, behind the counter, through a locked
door that you must hack open, is this audio diary.

Audio Diary #84 - "A Spy"
The edge of the theater balcony.

Audio Diary #85 - "Growing Up"
In the Triton Theater, follow signs up to the Projection 
Booth. Across from the booth room's door is a pile of 
rubble with the audio diary.

Audio Diary #86 - "A Secular Saint"
Go through the door to the left of the theater screen. The 
audio diary is at the end of the hallway.

Audio Diary #87 - "The Voice of the Self"
On the piano in the Piano Bar.

Audio Diary #88 - "Falling Into Place"
Inside the frozen Imago Gallery, near the entrance of the
same room with the Little Sister vent in the back. You'll
have to thaw some ice to grab the audio diary.

Audio Diary #89 - "Gotta Keep It Together"
Back of the J. Fischer Gallery, on a bookshelf partially 
covered by some rubble.

Audio Diary #90 - "A Plan"
At the very end of the level, in the newly opened security 
booth with Stanley Poole.

FONTAINE FUTURISTICS 

Audio Diary #91 - "Alone at Last"
Walk through the first door of this level and the audio 
diary is immediately to your left.

Audio Diary #92 - "Agnus Dei"
Pretty sure you won't miss this one. It's the password from 
Gil Alexander that you use to progress through the level.

Audio Diary #93 - "Means of Control"
After "Alex the Great" opens the door to the foyer, the
audio diary is on a couch immediately upon entering this
door, to the right of the corpse hanging from the wall.

Audio Diary #94 - "Prototype"
When you're first entering the Plasmid Showroom, go to the
end of the entrance hallway, and you can look through a hole
in the wall and see a corpse tied to a chair with a code
written in blood behind her. In the next area, with the water
on the ground near the harvest corpse, go through a locked door
with that code and you'll find the audio diary.

Audio Diary #95 - "Life After Sisterhood"
On the second floor of Fontaine Futuristics Tower. You'll 
notice it next to the Little Sister vent as soon as you 
climb the central stairs.

Audio Diary #96 - "A New Cognitive Model"
On the second floor, look for a hole in the western wall. 
Go through through, follow the passage to your left and drop
into the presentation room with the diary.

Audio Diary #97 - "Source of Volunteers"
Head to the Marketing Department of Fontaine Futuristics - 
the area with the Splicer board meeting that comes to life. 
The room to the left of this area is flooded with 
electrified water. The audio diary is on one of the 
submerged desks to your left as you come in.

Audio Diary #98 - "Goodbye to Fontaine"
Inside the Office of Frank Fontaine. Turn the boar head to 
reveal this audio diary.

Audio Diary #99 - "Abort the Experiment"
Upon entering the Plasmid Laboratory, the table with an audio
diary will be immediately upon your left. If you enter 
another underwater lock, you've gone too far, so turn back!

Audio Diary #100 - "Solving for X"
Under the circuit breaker on the north end of the lab you use
to restore power in the lab.