Quake

1. 
   Sink the Horror Electric

   Complete Quake Episode 1: Dimension of the Doomed in single player.
   22%
2. 
   Bottom of the Well

   Complete Quake Episode 2: The Realm of Black Magic in single player.
   14%
3. 
   Beneath the Blue Chambers

   Complete Quake Episode 3: The Netherworld in single player.
   12%
4. 
   The Last Unexplored Path

   Complete Quake Episode 4: The Elder World in single player.
   11%
5. 
   Indigestion

   Defeat Shub-Niggurath in single player.
   10%
6. 
   Gateway Traveller

   Complete Scourge of Armagon Episode 1: Fortress of the Dead in single player.
   7.4%
7. 
   Dominated Dominion

   Complete Scourge of Armagon Episode 2: Dominion of Darkness in single player.
   6.0%
8. 
   Arma-gone

   Complete Scourge of Armagon Episode 3: The Rift in single player.
   5.5%
9. 
   Overlord Overdone

   Complete Dissolution of Eternity Episode 1: Hell's Fortress in single player.
   5.1%
10. 
    Dragonslayer

    Complete Dissolution of Eternity Episode 2: The Corridors of Time in single player.
    4.6%
11. 
    The Year Zero

    Complete Dimension of the Past in single player.
    4.7%
12. 
    Vengeance Denied

    Complete Dimension of the Machine in single player.
    4.6%
13. 
    Vertical Vengeance

    Find the secret exit in Quake Episode 1: Dimension of the Doomed.
    13%
14. 
    Nevermore

    Find the secret exit in Quake Episode 2: The Realm of Black Magic.
    7.8%
15. 
    The Hot And Winding Road

    Find the secret exit in Quake Episode 3: The Netherworld.
    11%
16. 
    Into Sandy's City

    Find the secret exit in Quake Episode 4: The Elder World.
    4.0%
17. 
    Military Complex

    Find the secret exit in Scourge of Armagon Episode 1: Fortress of the Dead.
    4.3%
18. 
    The Gremlin's Domain

    Find the secret exit in Scourge of Armagon Episode 2: Dominion of Darkness.
    3.1%
19. 
    A Long Yard

    Find the secret exit in Scourge of Armagon Episode 3: The Rift.
    3.2%
20. 
    The House of Doom

    Find the secret exit in Dimension of the Past.
    3.2%
21. 
    Sandy's Room

    Find the secret exit in Dimension of the Machine.
    3.2%
22. 
    Secret Sleuth

    Find a secret area.
    57%
23. 
    The Well of Wishes

    Find the Well of Wishes in the Crypt of Decay.
    6.6%
24. 
    You're not supposed to be here!

    Find the secret message in Tur Torment.
    3.5%
25. 
    Friendly Fire

    Kill a monster with another monster's attack.
    53%
26. 
    Discharge

    In deathmatch, electrocute an enemy in water without dying.
    2.3%
27. 
    The Shambler Dance

    Kill a shambler before it is able to cast its lightning attack.
    24%
28. 
    A Close Shave

    Kill a shambler with an axe.
    8.6%
29. 
    The Painless Maze

    Complete E4M6: The Pain Maze on Nightmare without taking damage.
    2.2%
30. 
    Slipgate Pacifist

    Complete E1M1: The Slipgate Complex on Nightmare without firing a shot.
    3.7%
31. 
    Shub's Bud

    Complete Quake on Nightmare in single player.
    3.0%
32. 
    Scourge Done Slick

    Complete Scourge of Armagon on Nightmare in single player.
    2.2%
33. 
    Rogue Ranger

    Complete Dissolution of Eternity on Nightmare in single player.
    2.1%
34. 
    Otherworldly

    Complete Dimension of the Past on Nightmare in single player.
    2.2%
35. 
    Machinehead

    Complete Dimension of the Machine on Nightmare in single player.
    2.1%
36. 
    Disillusioned

    Complete Dawn of the Machine in single player.
    1.1%
37. 
    True Sight

    Complete Dawn of the Machine on Nightmare in single player.
    0.5%
38. 
    Bloody Nightmare

    Find the Death Knight's head.
    0.5%

Names, descriptions and icons are the game’s own, as Steam publishes them; the share is how many owners have unlocked each, from Steam's global figures for 38 of them.