SOLVED. Children's Fantasy - Evil being imprisoned in a pit

[Derek]

I only have vague recollections of this book - but I do remember that at the end of the book the evil being (I think it was a god-like entity - it didn't have a body) was imprisoned in some sort of pit.

This was the first book in a series. I probably read it around 2005, give or take a couple of years.

Some other tidbits that I remember (although these should be taken with caution, as I could be mixing things up with other books):

For some reason, I seem to remember that the main character (I think it was a girl?) was described as being really skinny, and at one point there was a description like "my father used to joke that he could fit a ring around my wrist" (although it is possible I'm confusing this with a different book...)

I think there were giants in the story somewhere.

I also seem to remember there being a ship involved...

[Derek]

I figured it out - it was the Land of Elyon series (The Land of Elyon Boxed Set) by Patrick Carman. Turns out I must have read the entire series, as some of the things I referenced don't happen until the later books.