Here is the full list of all 35 Avernum: Escape From the Pit achievements.
Purge a nefarious infiltrator from Silvar's sewers.
Slay 100 foes.
Escape the tunnels under Fort Avernum.
Learn a mage spell at level 3.
Learn 6 mage spells at level 3.
Learn 18 mage spells at level 3.
Learn a priest spell at level 3.
Learn 6 priest spells at level 3.
Learn 18 priest spells at level 3.
Get a dread curse. Then cure it.
Open a secret door.
Slay 1000 foes.
Dig up 5 caches.
Dig up 40 caches.
Have ten potions made.
Have fifty potions made.
Discover 10 locations of interest.
Discover 50 locations of interest.
Find the secret at the bottom of Lost Bahssikava.
Sss-Thsss will trouble Avernum no longer.
Steal the treasure from Gremlin's Gold.
The mayor of Formello lost something of great value. Recover it.
Purge a certain powerful demon from the Tower of Magi. Phew. Hope they stay out of trouble in the future.
Find something that lets you fly.
Reform a legendary blade from Avernum's past.
Join the Scimitar.
Meet the Archmage Erika.
Enter the Castle at last.
Avernum has five dragons. See if you can whittle that down a bit.
Destroy the demon Grah-Hoth, making Avernum safe from his menace at last.
Discover a route back to the surface world. There must be one somewhere.
Deliver harsh vengeance to the cruel tyrant who sent the Avernites into the underworld.
Complete all three game-winning quests in Avernum and never set the difficulty below Normal.
Complete all three game-winning quests in Avernum and never set the difficulty below Hard.
Complete all three game-winning quests in Avernum and never set the difficulty below Torment.