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