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.
Drown 20 Whorls.
Deal 5000 damage in one shot.
Collect 4 Keycards.
Find the robot janitor.
Unlock a golden chest with the Explorer's Key.
Kill a boss with 'Lights Out'.
Die 50 times.
Find the bloated survivor.
Bank 20,000 gold.
Collect 15 Monster Logs.
Survive 40 minutes.
Kill the Magma Worm, Wandering Vagrant, and Giant Stone Golem.
Pass a shrine 4 times in a row.
Fail a shrine 3 times in a row.
Defeat 20 lemurians in one playthrough.