Mine all 5 crystal types and have them in your home. You will need a mattock, so that makes the "Mattock" achievement a prerequisite for this.
- Pink crystal can be found in the caves near the surface.
- Dark crystal can be found in the caves near the Halls of Eternity.
- Blue crystal can be found in the cave with the face.
- Red crystal can be found in the central hall.
- White crystal can be found in the cave with a waterfall.