Scattered throughout the world of Half-Life 2 are 45 hidden Lambda caches — secret item stashes marked by the familiar Lambda logo. Some are easy to spot, others are sneakily tucked away, and a few require clever use of the gravity gun or environmental puzzles. If you’re aiming for the Lambda Locator achievement or just want some extra supplies, this guide walks you through each cache across every chapter in the game.

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Chapter: Point Insertion / Red Letter Day

1. Outside Dr. Kleiner’s Lab:
   • Near the vending machine door. There’s no physical cache to open — just walk near the door and look for the notification to confirm activation.

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Chapter: Route Kanal

2. Boarded Building (Train Jump):
   • After jumping the moving train, cross the tracks and enter the boarded-up building. Cache is under the Lambda icon.
3. Storage Container Crawlspace:
   • Mandatory cache — can’t progress without opening it.
4. Red Car Tunnel Access:
   • After the mounted gun, go left and hop the red car to find the cache.
5. Helicopter Encounter (Under Grate):
   • First helicopter attack — enter blue door, cache under the grate floor.
6. Pipe Crossing (Plank Drop):
   • See the symbol off to the right while crossing a pipe. Break the planks and drop to access the stash.
7. Curved Sewer Section (Ladder/Planks):
   • Find a detour left with a raised ladder and planks leading to the cache.
8. Radioactive Area (Pipe Walk):
   • Walk across pipes on the left to reach the stash on the far side.

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Chapter: Water Hazard

9. Tunnel Exit (Climb Up Ladder):
   • Cache is to your right shortly after the tunnel begins.
10. Red Barn (Barrel Drop):
    • Inside the barn, dislodge a barrel from above to drop the crate.
11. Circular Grate Pipe (Post-Gunship):
    • After troops are dropped, crawl inside pipe for this one.
12. Armored Car Rocket Attack (Hole by 2nd Vehicle):
    • Right side access tunnel under the second rocket-launching vehicle.
13. Counterweight Cache:
    • Use gravity gun to knock down bricks, lowering the cache.
14. Helicopter Mine Area (Opening on Left):
    • Crawl in after a mine drop sequence.
15. Flooded Pipe Section (Support Drop):
    • Break supports to drop the crate under the Lambda mark.
16. Slanted Side Passage (Green Graffiti):
    • Enter through a left-side gap marked with graffiti.
17. Bridge Fork (Take Left Before Twin Bridges):
    • Tucked away before the double bridges begin.
18. Boat Fork (Shelter at Right Path):
    • Final Water Hazard cache, found in a covered shelter.

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Chapter: Black Mesa East

19. Ladder Marked by Lambda (Start of Chapter):
    • Automatically triggers when you climb.

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Chapter: Ravenholm

20. Green Generators / Vent Duct:
    • Crawl through the air duct above the left green generator.
21. Car Trap / Fence Jump:
    • Ride the trap car, jump over the fence where the Lambda is.
22. Alley Drop / Plank Crossing:
    • Go through the rooftop hole marked with a symbol.
23. Cave Exit (Climb Boxes):
    • Above the mine exit — climb up for the last Ravenholm cache.

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Chapter: Highway 17

24. Red Shack Post-Bridge Jump:
    • After buggy drop and broken bridge jump.
25. Cellar by First Thumper:
    • Enter the cellar beside a house.
26. Gunship Fight Area (Blue Van):
    • Cache by a blue van after the second gunship encounter.
27. Gas Tank Area (Fence Jump with Barrel):
    • Use a barrel to climb the fence.
28. Rock Formations (Drop Ship Area):
    • Near large rocks to the left of departing drop ships.

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Chapter: Sandtraps

29. Battery Gatehouse (Roof Weapon Grab):
    • Use gravity gun to retrieve rifle charger from roof ledge.
30. Sand Bridge Metal Shack (Roof Climb):
    • Cache is on the ledge above the shack in the middle of the sands.

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Chapter: Nova Prospekt

31. Pillar Room / Sentry Turrets:
    • Find the small hole next to a Lambda marker.
32. Vortigaunt Chair Room (Tripwire Path):
    • Past the tripwire, open the cell with your gravity gun.
33. Laundry Room (Hallway to Cache Room):
    • Past the laundry machines and hallway on the right.

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Chapter: Entanglement

34. Vending Machine (Right After Alex):
    • Pull down objects from the top of the machine.

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Chapter: Anticitizen One

35. Dumpster Jump (Green to Blue):
    • Stack boxes to access cache near the fence.
36. Combine Shooter (Red Shack):
    • Hidden behind a metal sheet next to a red shack.
37. Underground Split Path (Crate Pull):
    • Use gravity gun to open crates.
38. Rubble Detour (Campfire Shelter):
    • Cache near a campfire after turning past a rubble wall.
39. Drop-Bridge Section (Wall Cache):
    • Hidden below a marked wall near a bridge drop.
40. Lower Floor Cache (Pull Through Fence):
    • Use gravity gun to pull cache through fence door.

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Chapter: Follow Freeman!

41. Generator Defense Room (Bottom Ledge):
    • Down near the ladder below the zombie horde.
42. Sewer Wall Hole (Crate Pull):
    • Use gravity gun from one side of the wall.
43. Pipe Platform Hop (Graffiti Marker):
    • Jump platform segments toward the symbol.
44. Lift Room (Red Room Wraparound):
    • Walk around the big red room before dropping to the final platform.

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Chapter: Our Benefactors

45. Strider Alley Stairwell Cache (Final Cache):
    • After fighting striders, under the overpass and down into an adjacent building.

Once all 45 caches are triggered (watch for the notification on screen), you’ll earn the Lambda Locator achievement. Good luck, and enjoy the exploration!