This is not so much an adventure as a very dangerous area to explore, suitable for quite high level characters (maybe about 8th-10th level) who may wish to investigate it. The Bog of Jelaneus, you see, is the remnants of an ancient and powerful empire which came to grief over 200 years ago, Jelaneus himself being one of the last emperors. Some say he brought down the wrath of the gods themselves, others say that he was performing some dark ritual that went very wrong... whatever the truth, this is all that remains of the Adurite Empire - and of course, as any brave adventurer knows, many wonders and riches might be found in such a place.
Characters travelling around the bog will come across certain locations, for which descriptions and other resources (including some of the wonderful photo-illustrations this publisher is known for!) are provided for the DM. Most will require further development before play, although there is an overview of what is to be found there and which monsters might take exception to the party's intrusion. There is also a large hex map for the party to plot their progress as they explore, and two maps (DM's and players') for a ruined city.
So for a party that fancies coming out of the dungeon and having a good squelch around a swamp in their ongoing search for fame and fortune, this should prove interesting - and potentially deadly. I don't think there's anything friendly there!