Here is the full list of all 15 Risk of Rain achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Unlock a golden chest with the Explorer's Key.
Deal 5000 damage in one shot.
Drown 20 Whorls.
Bank 20,000 gold.
Collect 15 Monster Logs.
Die 50 times.
Find the robot janitor.
Find the bloated survivor.
Collect 4 Keycards.
Kill a boss with 'Lights Out'.
Survive 40 minutes.
Pass a shrine 4 times in a row.
Kill the Magma Worm, Wandering Vagrant, and Giant Stone Golem.
Fail a shrine 3 times in a row.
Defeat 20 lemurians in one playthrough.