The Vault of Stars is a cavern where it is said you can see the night sky when you enter, even during the day. In fact, the main vault of this cavern is full of massive crystal growths that reflect and refract light illuminating the distant ceiling of the vault with sparkles and small rainbows of light.
The Vault has been used by various races throughout the years as a temple, a place of meditation and a warehouse. A clan of dwarves once claimed the Vault for a few generations, and errected a statue of the clan founder deep at the back of the main Vault and also built a small living area in a side passage to the North.
The current dwellers here, however, are less noble and friendly creatures. Four doppelgangers live here now, although they find the quarters quite cramped. They typically take the form of dwarves so they match their environment.
The lower level of the main vault has become the home to a Hill Giant that they lured in and trapped here (and they now feed her livestock or even the victims of their raids). If attacked from the edge of the pit, she will retreat back into the caves to wait out the attack.