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