The Catacombs of Vanaheim — Richard Denning

The Bifrost - the passageway between the Nine Worlds - is open and now Anna's village is under attack by creatures and horrors the villagers are not prepared to deal with. So now Anna and her companions must travel to Vanaheim, home to the Vanir: gods of wisdom and magic. There the young sorcerer, Wilburh, hopes to obtain a way to protect their village. It is not as easy as all that for Wilburh's magic is failing him and they find that the gods themselves are prisoners. To free them the children must enter the deadly Catacombs. In there they will need all their courage and skills just to survive.