Here are the achievements that affect the entire walkthrough:


Team Player
Don't kill any scientist or barney the entire game

This achievement is easily doable by avoiding killing any Barney or scientist. There's no special guide here - just avoid shooting these guys and reload game if you accidentally kill any (if they die to monsters, that doesn't affect the achievement).

The Right Tool in the Right Place
Get the crowbar

You'll get the the crowbar during Hazard Course.




Refreshing!
Drink a soda can

When you reach the security guard (after the elevator), there will be two vending machines. Press the "use" button on the machine, grab the soda can with your controller, and move it to your mouth.












Choo! Choo!
Drive a train

The train is at the very end of the Hazard Course, right after the place where you got the previous achievement. You will get the achievement automatically when you get onto it.




Safety First!
Complete the Hazard Course

Self-explanatory, cannot be missed

Black Mesa Inbound
Start the game

This is an unmissable achievement, and it should pop up as soon as you start the game.


How?
Jump out of the intro train

Use the teleport controls to get out of the train (i.e., onto the train tracks). You will be immediately teleported back into the train, so it is safe to do.

Warning!
Make sure to save at the start of the chapter (right after exiting train)


Bothersome
Speak to all scientists in the pre-disaster maps

The description is quite clear: you need to interact with every possible scientist in all maps before the incident. The game says there are 28 scientists in total.

This achievement can be bugged or easy to miss. If you didn't get it before entering the test chamber, load the save you made at the start and try again.

For me, it unlocked after I loaded the save and talked to a couple of scientists again. Maybe I missed someone, and it seems that the game tracks progress even on reload.


Trouble
Press the alarm button in the entrance area

Right after you enter the lobby, there would be a guard working on a computer. Under the table is an alarm button, interact with it.




Important Messages
Play with the laptop in the entrance area

In the same room, there is a big device standing in a corner. Interact with it, and a laptop will pop up, annoying the scientist.




Lights Out!
Turn off the lights in the office in the starting area

Right after the previous location, go straight (the door on the left leads to the computer room, the corridor on the right leads to the kitchen and HEV). There is a room with three scientists in it, and a light switch right next to the entrance. Turn off the lights, and you'll get the achievement.




The Magnusson Experiment
Do the microwave thing

On your way to pick up the HEV suit, go to the kitchen and interact with the microwave until the food explodes inside it.




Hello, Gordon!
Get the HEV suit

This one is impossible to miss - just get into the HEV suit.




Well Prepared
Grab the battery in your locker

Right after getting the HEV suit, open the locker with the name "Freeman" on it and pick up the battery on the floor.




A Small Cup
Find the small cup

In the same locker, on a shelf, there is a tiny coffee cup. Grab it with your hand and keep it with you for the next achievement.




The Smallest Cup!
Hold cup in front of Kleiner

Holding that small cup in your hand, you need to find a scientist with glasses (like in the screenshot), and put the cup to his mouth. He will say an Easter egg line, and you'll get the achievement.

NOTICE: After picking up the cup, you should walk only using locomotion. Teleporting will return the cup back to the shelf.



Troll
Get the "Bothersome", "Important Messages", "Trouble", "Magnusson Experiment", and "Lights Out!" achievements

This achievement should be unlocked automatically when you do all the mentioned achievements. Usually, that means it will unlock after completing "Bothersome," right before the test chamber.

CPR Expert
Your moral support saved them!

Right after the incident, you will see scientists performing CPR on a guard. Wait until the guard stands up, and you will get the achievement.




Unforeseen Consequences
Make the hanging scientist in the entrance area fall to their death

In the entrance area where you played with the alarm and laptop in the previous chapter, use the crowbar to hit the blue screen near the door to unlock the way to the monorail station. You will see a scientist standing on the damaged bridge. Step onto it, then immediately step back and watch the scientist die to unlock the achievement.




Baseballed
Hit a headcrab with a melee attack in mid-air

The first chance to get it will be in the starting lobby. After you get through this vent, go into the computer room. Hit the headcrab with a crowbar mid-air and you're good.

You'll have multiple chances to get that achievement later in the game if you missed it.




Pet the doggo!
Touch a houndeye without hurting it

Soon after the previous achievement, you'll meet houndeyes. Gently touch that cute alien doggy to get the achievement. It may require multiple tries to register.

You'll have multiple chances to get that achievement later in the game if you missed it.




Fascinating Specimen
Pick up an alien gib

You will have a lot of chances to unlock this achievement during gameplay. One option is to hit these houndeyes you've met with crowbar until they explode and pick up the gib.


Catch!
Throw a gib at a scientist or barney

In the same place where you met the houndeyes, a scientist is waiting. After you have killed the houndeyes, ask him to follow you so that he won't freak out and run away. Then, wait for human gibs to be thrown from the ventilation above and throw them at him.

Continue throwing the human gibs until you unlock the achievement. If the achievement is not unlocked after the 10th try, reload the previous save file and try again.

Achievement is extremely glitchy and unreliable, but this particular place seems more or less stable.

OSHA Violation
Get killed by the eletric ceiling light

At the start of the chapter, after the elevator, run and die under the wires that hang from the ceiling. There can be a glitch that wire doesn't kill you instantaneously. In that case, reload the last save and try again.




Look, Gordon! Ropes!
Push or lure a scientist into a barnacle

In that room on the screenshot, after you turn off the light, interact with the scientist so he will follow you. Bring him close to the barnacle and push him into it.

I suggest saving and then loading the game for that achievement; otherwise, it may impact the 'Team Player' progress (unconfirmed).




Duck!
Get killed by the fan in the vents

Right after the previous office and corridor with broken light, you'll get to a room filled with electrified water. Crawl into the vents and die to the rotating fan there.

For the next achievements, as soon as you get into the elevator from the elevator shaft, don't press the button!. Make a hard save file when you get in, and quick save as well. You'll need to reload it multiple times.

After creating saves, you can exit the elevator and see a scientist shouting, "FOR GOD'S SAKE OPEN THE SILO DOOR".

On this scene, you'll have three ways to act, each one leading to a different achievement.





Doomed!
Fail to save the "we're doomed" scientist

The first achievement in this chapter is to just stay there and watch the scientist die on the tripmine. Reload the save in the elevator to get the next achievements.


Doomed No More!
Save the "we're doomed" scientist


Doomed? Skip!
Skip the whole "We've Got Hostiles" chapter

For that achievement, you need to use a speedrun technique of completely skipping the level. It's a little bit tricky and probably will require several attempts, but it's completely doable.

Be advised: in the middle of that sequence, it's better to create a separate save file for the next achievement.

Here's the basic way to do it:

• Load the save inside the elevator (before you press the button to exit it).
  
• Run to the window and stay right in front of the scientist, blocking his way to the tripmine.
  
• Spam "interact" to him until he agrees to follow you.
  
• Push him to the door that leads to the security room.
  
• Push him into that room.
  
• Press the big red button to open the silo door.
  
• Make a separate save file for the next achievement.
  
• Push the scientist to the room door again so he will open it for you.
  
• Go to the next level. The achievement should pop out as soon as the next level is loaded (you'll be standing in front of the barricade).
  
• Also, the "Doomed No More!" achievement should unlock at the same time.

Note: there's technique that relies on shooting scientist to stop him and open security room door - DON'T USE IT. That would scare scientists, he'd refuse to follow you, and despite the fact that you can skip chapter in that way - achievement wouldn't work. It requires scientist that agreed to follow you.

Video guide (not mine):


Perfect Balance
Complete We've Got Hostiles without activating any laser traps or trip mines

That achievement requires you to go through the entire chapter without triggering any laser traps or trip mines, which seems extremely difficult. However, it actually requires you to visit at least one chapter map (except the starting one), so there's a little trick to get the achievement.

Here's a step-by-step guide:

• Load the save file that you created in the previous achievement in the security room.
  
• Teleport into the vent with blood around it and go through the vent until you get to a space with a ladder.

• Drop down and go through the another vent (it may be glitchy) until you reach another open space with a fan above you.
  
• Inside that space, first teleport onto the tiny surface in front of the bars shown in the screenshot. It may require some tries, but it's doable. You may need to jump and teleport mid-air.

• After that, teleport to the ledge right above you and go into the vent.

• After going inside the vent for a few meters, you'll notice a level change.
  
• Turn back, head to the security room, go through the silo door, and into the Blast Pit chapter. The achievement should unlock on level load.

Perfect Landing
Fly directly into the pipe from the train

This one is tricky. At the beginning of the chapter, there is a train that loses control and sends you flying into green water. You need to land on the pipe located to the right, near the entrance, or close enough to it.

Following setup helped me:

• Movement is set to HMD (move where you look)
  
• Look straight ahead
  
• Right before impact, start strafing to the right
  
• Upon impact, press the jump button

That required some practice, but it's possible to do.



How Did The Pipes Survive?
Blow up all the bridges in Blast Pit

There are three bridges in the chapter that lead to the rocket test chamber. Explode them all to get the achievement.













Sneaky I
Never get noticed by the tentacles

Another tricky achievement. It would be useful to create a static save when you first reach the control room and see how the tentacle kills the scientist.

Here's a basic guide:

• You have to stay unnoticed by the tentacle in the rocket chamber.
  
• Grenade explosions do not count as sounds you make and can distract the tentacle from your sounds.
  
• Use the teleport to avoid making sounds in general.
  
• On your way down: explode the crates that block the ladder; otherwise, you'll be screwed on your way up.
  
• On your way down: use the teleporter to teleport down and to go through barricaded doors.
  
• On your way up: use the teleporter to reach the ladder, throw a grenade to distract the tentacle, and then immediately after the explosion, start climbing the ladder and dismount it before you get noticed by the tentacle.

If you did everything properly, the achievement should unlock when you press the "TEST FIRE" button. If it didn't unlock, you need to start from scratch.




Bad Design
Solve the Blast Pit fan puzzle

On your way to turn on the oxygen and fuel, you'll come across the fan puzzle. Turn it on and get up safely.

If you're struggling with it, there's an option in HLVRConfig.exe to make the fan non-solid, so it won't kill you. Config is located in Immersion -> VR Compatibility -> Make Blast Pit fan non-solid.




It's a Trap!
Use the broken elevator

On your way to turn on the power, you'll come across a yellow elevator surrounded by houndeyes and one bullsquid. Use it.

There are two ways to complete this chapter, each one leads to different achievements. Save before the start of the chapter, when the pipe you walk through breaks, and you land in the room with some boxes and a headcrab.




Smells Like BBQ
Fry the Gargantua

Just go through the chapter without skipping too much with the teleporter. Turn on the power, go back, flip the switch, and fry the Gargantua with electricity in the room in the picture.












Tripmines? Ladders!
Skip the whole "Power Up" chapter

Load the the save you made at the start of the chapter, run straight to the right in room with Gargantua, jump and teleport at the barricade to marked point. Then just teleport to the other side of barricade.

There is also option to use tripmines as ladders, as achievement suggests. It's easy to find on YouTube by "Power Up skip" search query.

Off A Rail
Complete "On A Rail" without ever using a train

Achievement will unlock only at the end of the chapter.

If you skipped the previous chapter for the achievement, you'll start doing this one automatically. Just avoid using any trains. The achievement will unlock when you go deeper into the tunnel, passing by the old red train.





Look up!
Get sniped

When you reach the surface for the first time, there is a sniper behind the camouflage net. Let him kill you.




To Infinity And Beyond
Launch the satellite rocket

This achievement is probably unmissable unless you're doing some hacky speedrun. Just press the button to launch the satellite into space.

These Aren't Trains
Try to use the trash compactors as trains

At the end of the chapter, you'll be thrown into a trash compactor. Climb up using the boxes, get on top of the compactor walls, and try to interact with them - they're technically trains.

Parental Instinct
Save the barney from running into the barnacle

This achievement may be bugged; it unlocked for me after the guard started running, died to a barnacle, and I loaded a quick save.

Right after the surface part of the chapter, you'll reach a security guard fighting with headcrabs. For this achievement to unlock:

• The security guard has to start running.
  
• He has to be alive 5 seconds after he started running.

Either block his way, or kill the barnacles that's inside the corridor.




Möbius trip
Repeat the conveyor loop

Later in the chapter, you will enter a large room with multiple conveyor belts. To unlock this achievement, you need to take a full trip on the belts, take the wrong turn, and return to the start. An easier way to achieve this is to go in the opposite direction as soon as you enter the room on the wide belt and drop to the first narrow one. The trigger for the achievement is located where this belt connects with another one in the corner.

Rigorous Research
Kill all the aliens with all the experiments

There are two experiment rooms in that chapter, one after the beginning and the second after the lobby, upstairs. You need to kill all 5 headcrabs in the first room and 7 headcrabs in the second room.




Effective Research
Kill a soldier with an experiment

Right after you kill the headcrabs in the first experiment room, a soldier will spawn behind the door. Lure him into the room and press the button again.












Research At All Costs
Kill a barney or scientist with an experiment

WARNING: Save before attempting this achievement and load after getting it, otherwise you will break your "Team Player" achievement progress.

After the first experiment room, behind the corner, barney is waiting for you. Ask him to follow you, lead him into the experiment room, and press the button again.












Precision Surgery
Kill a scientist with the instruments

WARNING: Save before attempting this achievement and load after getting it, otherwise you will break your "Team Player" achievement progress.

During the progression of the chapter, you will come across a room with three scientists and a scary-looking machine with multiple saws. Stop the machine using the control panel, ask one of the scientists to follow you, and start the machine again when he is inside.

What a View I
Reach the cliffs

This achievement is impossible to miss; just continue until you reach the cliffs.




Sneaky II
Surface behind the tank

After the cliffs area, you need to navigate through the pipes in a specific order to reach the surface behind the tank. Do not climb up the ladder anywhere else!

• Turn left.
  
• In the area with water, go straight to another pipe.
  
• Turn left again.
  
• Climb up the ladder to get behind the tank.

It's Not Cheating
Gain more than 1000 HP from a negative damage door

Door is located near the end of the chapter. This is a known bugged door from the original Half-Life that does negative damage to the player, increasing their health. As the achievement states, you need to get 1000 HP from that door.

In order for this door to work in this mod, you actually need to enable cheats in the console by typing these two commands:
Without them, the door won't heal you or cause any damage.

So, the achievement itself:
- Rescue the security guard, who opens the door for you, from the building.
- Type the aforementioned commands in the console.
- Go with the security guard to the door.
- Get stuck in it and wait for some time until the achievement unlocks.

The easiest way to get crushed by the door is actually to teleport through that door and wait behind it. By spamming teleport + run at the corner of the door, you can get to the other side and wait there. Arrow on the second screenshot marks where you should aim with teleport.

Fire In The Hole!
Explode the Gargantua with airstrikes

This achievement is self-explanatory. Right after the negative damage door, you will get into a tunnel with a Gargantua. Run from it, jump to the elevated silo with an interactive map on it, and call an airstrike on the Gargantua when it gets out of the tunnel.

I found it easy to aim at the first gates (on the screenshot) and catch it there.

No achievements

What a View II
Reach Xen

This achievement is impossible to miss and will unlock as soon as you teleport to Xen from Lambda Core.

No achievements.

No achievements.

What is that thing?
Meet the Nihilanth

This one is unmissable, meet the final boss.


Explorer
Get teleported to all of Nihilanth's spaces

There are four spaces where Nihilanth teleports you, in order:

• Vertical shaft with ledges and bridges, filled with Controllers.
  
• Vertical shaft expanding at the bottom, with Controllers and rocks rising to the top.
  
• Big space with a pool and Vortigaunts.
  
• Big space with a pool and Gargantua.

For the achievement to unlock, you need to be teleported to the last space with the Gargantua by the Nihilanth teleporter. Just keep walking into his teleporters until you get the achievement.






















Sky Baby go brrr
Beat the Nihilanth

This one is unmissable as well.

Time To Choose
Face the G-Man

This achievement is unmissable and will unlock after killing Nihilanth.


Limitless Potential
Join the G-Man


Unwinnable Battle
Don't join the G-Man

At the end of the game, you will get a choice - either step into the green teleporter and join G-Man (Limitless Potential), or refuse his offer (Unwinnable Battle). Save and do both of them to get the achievements.



Congratulations! You've completed the game.