Here is the full list of all 40 Six Ages: Ride Like the Wind achievements.
Beren the Swift wed Redalda
See a god
Make peace between believers and disbelievers in Cenala
Have a hero accomplish their destiny
Your clan had to disband
The game ends in defeat
Win at Easier difficulty without restoring to a previous save
Win at Normal difficulty without restoring to a previous save
Win at Hard difficulty without restoring to a previous save
Win at Harsh difficulty without restoring to a previous save
Win the game at the Easier difficulty level
Win five times
Win ten times
Win the game
Win at the Hard difficulty level
Win the game at the Harsh difficulty level
Win the game without anyone starving
The wedding was interrupted
Hoard 25 treasures
Defeat a demonic army
Send an emissary to every clan
End a feud
Build every fortification
Succeed at every Otherworld ritual
Split the Clan
Send a caravan to every clan
Explore caves
Gain the allegiance of ten spirits
Learn every mystery
Return to the Traveling Stone
Explore the Valley and beyond
Learn every myth
Convince all Rider clans to reject the Cenala heresy
Make peace with your ancestral enemy
Build a shrine to every deity
Convince all Rider clans to acknowledge the Cenala revelation
Select a Trickster to lead the clan
Visit every Ram land
Tame the Black Eel and Oslira Rivers
Discover the easter egg