I have gotten every crystal except the one in the capital city.  I can't walk in the front door, but I can't figure out how to get in.  The village to the south I can't interact with anyone or anything.  

In the world map, there is a small tent next to the capital city.

Go into the tent and talk to the people on the map.

She will take you to the capital (the Glades), then complete the story of the Glades saving the princess, and you can return to the capital.