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