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