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