This 64-page sourcebook is an introduction and overview of six different "mega-dungeons" in Golarion, the setting for the Pathfinder RPG. For each megadungeon, a sideview schematic shows how the various levels are arranged and connected. Next, each level (usually arranged from easiest to hardest) is given a one-paragraph description and ideas for the types of threats present there. Each megadungeon also includes a write-up of a new monster, a trap, and a new magic item or spell found within. A couple of adventure hooks to lure PCs to the megadungeon complete each section.
The six megadungeons covered are:
* Candlestone Caverns, a complex in rural Andoran occupied by various monstrous humanoids (especially kobolds) and linked to the Darklands.
* Gallowspire, the famous fortress in Ustalav that contains the power of the undead lich The Whispering Tyrant. The backstory here is fascinating and the description is quite evocative for would-be undead slayers.
* Hollow Mountain, a peak on an island off the coast of Varisia that was the capital of the Thassilonian Runelord of Wrath's domain. The book's great cover depicts one of her sinspawn.
* The Pyramid of Kamara, a foreboding pyramid in Osirion that is the tomb of a Rovagug-worshipping pharaoh. I quite liked how the top level is occupied by con-artists who stage fake mummy attacks for the entertainment of tourists.
* The Red Redoubt of Karamoss, an ancient subterranean structure near Absalom that was the home of a wizard who built technological marvels based on research in Numeria. Robots and techno devices galore still exist within.
* The Zolurket Mines, an ancient dwarven mine corrupted by a necromantic mineral that has turned the original miners into ghouls!
The important thing about this book is that, as cool as the outlines are, none of the megadungeons are anywhere near being playable without a tremendous amount of work by a GM in producing level maps, stocking those levels with monsters, and figuring out treasure. Also this is another high-quality Paizo product, it's really only for those GMs who have a LOT of time on their hands but need inspiration.