This is just a rough description of where you need to go.
1- Explore Skara Brae until your party is level 3-5. Enter houses to get some free loot.
Places to look for:
- The shop – Only basic weapons can be purchased at start, but the only place to sell stuff.
- Rosco´s – Until later in game the only viable place to restore spell points.
- Review Board – Get level ups ,buy new spell and change mage class.
2- When you feel strong enough head south from the guild and beat the samurai statue. Behind it to the left is a bar that sells wine, order some to enter the wine cellar. Explore and work yıur way till you reach sewers level 2. Behind a light you find a hint with the name of the mad god.
3- On central plaza is the temple of the mad god tell the priest its name. Explore and find the spectre on the lowest level. Kill it to get it’s eye.
4- Take the eye to harkyn´s castle in the north west of skara brae behind some golem and a dragon statue. Make your bard sit on the throne to open secret door. Make sure you find and take the crystal sword with you, equip it on all who can use it.
You can get it severall times just leave and re-enter. On level 3 you can find the statue of the mad god. Fight it to get tele to kylearan´s tower.
5- In kylearan´s tower you will face a crystal golem. Deathblow with crystal sword will perma kill it. You get onyx key from kylearan.
6- Go down to sewer 3 and find the stair leading up to mangar´s tower. Enter and kill magar on level 5.