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