This is a reimagining of the original I6: Ravenloft module to be set in a normal campaign world. This is not a reimagining or addition to the Ravenloft campaign world.
From the Back of the Book:
The Expedition to Castle Ravenloft campaign adventure updates the original 1st Edition Ravenloft module, retaining the Gothic flavor and familiar elements while expanding and reimagining some of the locations to create a deeper, richer adventure experience.
This campaign adventure is designed for characters of levels 6-10 and features new, easy-to-use combat encounter format. This book also presents new magic items, feats, and prestige classes for player characters.