Kill an enemy with a toilet.
Discover the hidden singing vortigaunt cave in chapter Water Hazard.
Cross the antlion beach in chapter Sandtraps without touching the sand.
Beat Episode One firing exactly one bullet. Grenade, crowbar, rocket, and Gravgun kills are okay!
Get 25 headshots as a Sniper.
Use flares to light 15 zombies on fire.
Kill five barnacles with one barrel.
Continue playing to unlock this secret achievement.
Win 20 games.
Win 2Fort with a shutout.
Win Well in 5 minutes or less.
Play a complete game on every map.
Win Hydro without giving up a capture.
Play a complete round with every class.
Successfully defend Gravel Pit without giving up a capture.
Accumulate 10 turret kills with a single turret.
Trick an opposing medic into healing you.
Get five kills in a row without dying.
Get five revenge kills.
Successfully defend Dustbowl without giving up a capture.
Help Griggs and Sheckley hold off the antlion invasion inside the mine shaft.
Run over 20 enemies with the car in Episode Two.
Defeat the chopper in Episode Two without any misses.
Find every radar cache in chapter Under The Radar.
Unlock the rocket launcher lambda cache in chapter Under The Radar.
Beat DOG in a race to the White Forest base.
Send the garden gnome into space.
Save all buildings outside the missile silo from destruction.
Kill a Hunter with its own flechettes.
Acquire the fully powered Aperture Science Handheld Portal Device.
Do whatever it takes to survive.
Make the correct party escort submission position decision.
Complete Portal.
Fall 30,000 feet.
Jump 300 feet.
Beat two Portal advanced maps.
Beat four Portal advanced maps.
Beat all six Portal advanced maps.
Earn bronze medals on all Portal challenges.
Earn silver medals on all Portal challenges.
Earn gold medals on all Portal challenges.
Play in a game with seven or more players from your friends list.
Accumulate 1000 total kills.
Accumulate 25000 heal points as a Medic.
Set five enemies on fire in 30 seconds.
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Gain command of a squad of rebels in the uprising.
Detach security cameras from the walls.
Knock down a turret with another turret.
Kill 30 enemies with thrown physics objects.
Kill an enemy by planting a hopper mine.
Kill five enemies with a Manhack.
Kill a Combine soldier with his own grenade.
Kill five enemies with the same energy ball.
Kill an Elite Soldier with his own energy ball.
Steal a Zombine's grenade.
Escape the apartment block raid.
Break the mini-teleporter in Kleiner's lab.
Get the crowbar.
Get the airboat.
Get the airboat's mounted gun.
Destroy the hunter-chopper in Half-Life 2.
Find the HEV Suit Charger faceplate in Eli's scrapyard.
Get the Gravity Gun in Black Mesa East.
Use DOG's ball to make a basket in Eli's scrapyard.
Play through Ravenholm using only the Gravity Gun.
Kill 3 enemies using the crane.
Pin a soldier to the billboard in chapter Highway 17.
Destroy six gunships in Half-Life 2.
Use the antlions to kill 50 enemies.
Survive the second turret standoff in Nova Prospekt.
Get through the toxic tunnel under City 17 in Half-Life 2.
Survive the generator plaza standoff in chapter Anticitizen One.
Kill all of the snipers in City 17.
Shut down the supression device by disabling its generators.
Survive the rooftop strider battle in the ruins of City 17.
Find all lambda caches in Half-Life 2.
Make it to the bottom of the Citadel's main elevator shaft in one piece.
Contain the Citadel core.
Contain the Citadel core without killing any stalkers.
Use the cars to squash 15 antlions in Episode One.
Survive long enough to get on the parking garage elevator.
Help Alyx snipe 30 enemies in Episode One.
Destroy the gunship in the hospital attic.
Don't let any citizens die when escorting them to the escape train.
Escape City 17 with Alyx.
Kill an acid antlion worker.
Squish every antlion grub in Episode Two.
Find and break every web cache in Episode Two.
