Here is the full list of all 18 Solstice achievements.
Experience all possible endings.
Abandon your goals.
Save the day like a true hero.
Receive assistance from someone who trusts no one.
Seek magic and power hard enough.
No dog should see this...
Let Yani be the doctor for once.
Just relax and enjoy the baths.
Leave a mark on the wasteland.
Bring the murderer to justice.
Keep it warm and natural.
Let the Winter win.
Make the final choice.
Get intimate with an ex-killer.
Find out what happened to Lev.
Play it safe when talking to strangers.
Make a promise to someone you barely know.
Pay attention to Galen's mentor.